Dashboard refresh (logs, storage, network, object store, docs) (#835)

## Summary

This PR adds a session management service, several new dashboard pages, and a number of infrastructure improvements.

### Sessions Service
- `SessionsServiceClient` in `zenutil` announces sessions to a remote zenserver with a 15s heartbeat (POST/PUT/DELETE lifecycle)
- Storage server registers itself with its own local sessions service on startup
- Session mode attribute coupled to server mode (Compute, Proxy, Hub, etc.)
- Ended sessions tracked with `ended_at` timestamp; status filtering (Active/Ended/All)
- `--sessions-url` config option for remote session announcement
- In-process log sink (`InProcSessionLogSink`) forwards server log output to the server's own session, visible in the dashboard

### Session Log Viewer
- POST/GET endpoints for session logs (`/sessions/{id}/log`) supporting raw text and structured JSON/CbObject with batch `entries` array
- In-memory log storage per session (capped at 10k entries) with cursor-based pagination for efficient incremental fetching
- Log panel in the sessions dashboard with incremental DOM updates, auto-scroll (Follow toggle), newest-first toggle, text filter, and log-level coloring
- Auto-selects the server's own session on page load

### TCP Log Streaming
- `LogStreamListener` and `TcpLogStreamSink` for log delivery over TCP
- Sequence numbers on each message with drop detection and synthetic "dropped" notice on gaps
- Gathered buffer writes to reduce syscall overhead when flushing batches
- Tests covering basic delivery, multi-line splitting, drop detection, and sequencing

### New Dashboard Pages
- **Sessions**: master-detail layout with selectable rows, metadata panel, live WebSocket updates, paging, abbreviated date formatting, and "this" pill for the local session
- **Object Store**: summary stats tiles and bucket table with click-to-expand inline object listing (`GET /obj/`)
- **Storage**: per-volume disk usage breakdown (`GET /admin/storage`), Garbage Collection status section (next-run countdown, last-run stats), and GC History table with paginated rows and expandable detail panels
- **Network**: overview tiles, per-service request table, proxy connections, and live WebSocket updates; distinct client IPs and session counts via HyperLogLog

### Documentation Page
- In-dashboard Docs page with sidebar navigation, markdown rendering (via `marked`), Mermaid diagram support (theme-aware), collapsible sections, text filtering with highlighting, and cross-document linking
- New user-facing docs: `overview.md` (with architecture and per-mode diagrams), `sessions.md`, `cache.md`, `projects.md`; updated `compute.md`
- Dev docs moved to `docs/dev/`

### Infrastructure & Bug Fixes
- **Deflate compression** for the embedded frontend zip (~3.4MB → ~950KB); zlib inflate support added to `ZipFs` with cached decompressed buffers
- **Local IP addresses**: `GetLocalIpAddresses()` (Windows via `GetAdaptersAddresses`, Linux/Mac via `getifaddrs`); surfaced in `/status/status`, `/health/info`, and the dashboard banner
- **Dashboard nav**: unified into `zen-nav` web component with `MutationObserver` for dynamically added links, CSS `::part()` to merge banner/nav border radii, and prefix-based active link detection
- Stats broadcast refactored from manual JSON string concatenation to `CbObjectWriter`; `CbObject`-to-JS conversion improved for `TimeSpan`, `DateTime`, and large integers
- Stats WebSocket boilerplate consolidated into `ZenPage.connect_stats_ws()`

1 files changed, 421 insertions, 29 deletions

diff --git a/src/zenserver/frontend/html/zen.css b/src/zenserver/frontend/html/zen.css
index 49a1e6d21..b4f7270fc 100644
--- a/src/zenserver/frontend/html/zen.css
+++ b/src/zenserver/frontend/html/zen.css
@@ -27,6 +27,7 @@
 		--theme_bright:			#1f2328;
 		--theme_faint:			#6e7781;
 		--theme_border_subtle:	#d8dee4;
+		--theme_highlight:		#b8860b44;
 	}
 }
 
@@ -54,6 +55,7 @@
 		--theme_bright:			#f0f6fc;
 		--theme_faint:			#6e7681;
 		--theme_border_subtle:	#21262d;
+		--theme_highlight:		#e3b341aa;
 	}
 }
 
@@ -81,6 +83,7 @@
 	--theme_bright:			#1f2328;
 	--theme_faint:			#6e7781;
 	--theme_border_subtle:	#d8dee4;
+	--theme_highlight:		#b8860b44;
 }
 
 :root[data-theme="dark"] {
@@ -106,6 +109,7 @@
 	--theme_bright:			#f0f6fc;
 	--theme_faint:			#6e7681;
 	--theme_border_subtle:	#21262d;
+	--theme_highlight:		#e3b341aa;
 }
 
 /* theme toggle ------------------------------------------------------------- */
@@ -214,34 +218,6 @@ button {
 	}
 }
 
-/* service nav -------------------------------------------------------------- */
-
-#service_nav {
-	display:			flex;
-	align-items:		center;
-	gap:				4px;
-	margin-bottom:		16px;
-	padding:			4px;
-	background-color:	var(--theme_g3);
-	border:				1px solid var(--theme_g2);
-	border-radius:		6px;
-
-	a {
-		padding:			6px 14px;
-		border-radius:		4px;
-		font-size:			13px;
-		font-weight:		500;
-		color:				var(--theme_g1);
-		text-decoration:	none;
-		transition:			color 0.15s, background 0.15s;
-	}
-
-	a:hover {
-		background-color:	var(--theme_p4);
-		color:				var(--theme_g0);
-		text-decoration:	none;
-	}
-}
 
 /* links -------------------------------------------------------------------- */
 
@@ -358,6 +334,207 @@ a {
 	}
 }
 
+/* sessions ----------------------------------------------------------------- */
+
+.sessions-section {
+	display:				flex;
+	flex-direction:			column;
+	height:					calc(100vh - 80px);
+}
+
+.sessions-layout {
+	display:				flex;
+	gap:					1.5em;
+	align-items:			flex-start;
+	flex-shrink:			0;
+}
+
+.sessions-table {
+	flex:					1;
+	min-width:				0;
+}
+
+.sessions-table .zen_table > div > div {
+	text-align:				right;
+}
+
+.sessions-table .zen_table > div > div:nth-child(2) {
+	font-family:			'SF Mono', 'Cascadia Mono', Consolas, 'DejaVu Sans Mono', monospace;
+}
+
+.sessions-detail {
+	width:					600px;
+	flex-shrink:			0;
+	font-size:				13px;
+}
+
+.sessions-detail h3 {
+	margin:					0 0 0.6em 0;
+	font-size:				13px;
+	text-transform:			uppercase;
+	letter-spacing:			0.5px;
+	color:					var(--theme_g1);
+}
+
+.sessions-detail .zen_table {
+	margin-bottom:			1em;
+}
+
+.sessions-detail-placeholder {
+	color:					var(--theme_g1);
+	font-style:				italic;
+}
+
+.sessions-selected {
+	background-color:		var(--theme_p3) !important;
+}
+
+.sessions-log-panel {
+	margin-top:				12px;
+	border:					1px solid var(--theme_g3);
+	border-radius:			6px;
+	overflow:				hidden;
+	display:				flex;
+	flex-direction:			column;
+	flex:					1;
+	min-height:				200px;
+}
+.sessions-log-header {
+	display:				flex;
+	align-items:			center;
+	padding:				6px 12px;
+	background-color:		var(--theme_bg1);
+	border-bottom:			1px solid var(--theme_g3);
+	flex-shrink:			0;
+}
+.sessions-log-title {
+	font-size:				12px;
+	font-weight:			600;
+	text-transform:			uppercase;
+	letter-spacing:			0.5px;
+	color:					var(--theme_g1);
+}
+.sessions-log-filter {
+	margin-left:			12px;
+	padding:				6px 12px;
+	font-size:				14px;
+	font-family:			inherit;
+	border:					1px solid var(--theme_g2);
+	border-radius:			6px;
+	background:				var(--theme_bg1);
+	color:					var(--theme_bright);
+	outline:				none;
+	width:					200px;
+}
+.sessions-log-filter:focus {
+	border-color:			var(--theme_ln);
+	background:				var(--theme_bg0);
+}
+.sessions-log-filter::placeholder {
+	color:					var(--theme_g1);
+}
+.sessions-log-body {
+	flex:					1;
+	min-height:				0;
+	overflow-y:				auto;
+	font-family:			'SF Mono', 'Cascadia Mono', Consolas, 'DejaVu Sans Mono', monospace;
+	font-size:				12px;
+	line-height:			1.5;
+	padding:				4px 0;
+	background-color:		var(--theme_bg0);
+}
+.sessions-log-empty {
+	color:					var(--theme_g1);
+	font-style:				italic;
+	padding:				8px 12px;
+	font-family:			inherit;
+}
+.sessions-log-trimmed {
+	color:					var(--theme_g1);
+	font-style:				italic;
+	padding:				2px 12px;
+	font-size:				11px;
+}
+.sessions-log-line {
+	padding:				0 12px;
+	white-space:			pre;
+	display:				flex;
+	gap:					8px;
+}
+.sessions-log-line:hover {
+	background-color:		var(--theme_bg1);
+}
+.sessions-log-ts {
+	color:					var(--theme_g1);
+	flex-shrink:			0;
+}
+.sessions-log-level {
+	flex-shrink:			0;
+	min-width:				4em;
+	font-weight:			600;
+}
+.sessions-log-level-info  { color: var(--theme_ln); }
+.sessions-log-level-warn  { color: #d29922; }
+.sessions-log-level-error { color: #f85149; }
+.sessions-log-level-debug { color: var(--theme_g1); }
+.sessions-log-msg {
+	white-space:			pre-wrap;
+	word-break:				break-all;
+}
+.sessions-log-data {
+	color:					var(--theme_g1);
+	white-space:			pre-wrap;
+	word-break:				break-all;
+}
+
+.sessions-self-pill {
+	display:				inline-block;
+	font-size:				0.7em;
+	font-weight:			600;
+	padding:				1px 6px;
+	margin-right:			6px;
+	border-radius:			8px;
+	background-color:		var(--theme_p4);
+	color:					var(--theme_g0);
+	vertical-align:			middle;
+}
+
+.objectstore-bucket-detail {
+	grid-column:			1 / -1;
+	padding:				8px 16px;
+	background-color:		var(--theme_bg1);
+	border-top:				1px solid var(--theme_g3);
+	font-size:				0.9em;
+}
+.objectstore-objects-table {
+	width:					100%;
+	border-collapse:		collapse;
+}
+.objectstore-objects-table th {
+	text-align:				left;
+	font-weight:			600;
+	padding:				4px 8px;
+	border-bottom:			1px solid var(--theme_g3);
+	color:					var(--theme_g1);
+	font-size:				0.85em;
+}
+.objectstore-objects-table td {
+	padding:				2px 8px;
+	font-family:			var(--font_mono);
+	font-size:				0.85em;
+}
+
+.sessions-pager {
+	display:				flex;
+	align-items:			center;
+	gap:					8px;
+	margin-top:				8px;
+}
+.sessions-pager-label {
+	font-size:				0.85em;
+	opacity:				0.7;
+}
+
 /* expandable cell ---------------------------------------------------------- */
 
 .zen_expand_icon {
@@ -560,6 +737,20 @@ zen-banner {
 	margin-bottom:		24px;
 }
 
+zen-banner:has(+ zen-nav) {
+	margin-bottom:		-1px;
+}
+
+zen-banner:has(+ zen-nav)::part(banner) {
+	border-bottom-left-radius:	0;
+	border-bottom-right-radius:	0;
+}
+
+zen-banner + zen-nav::part(nav-bar) {
+	border-top-left-radius:		0;
+	border-top-right-radius:	0;
+}
+
 /* error -------------------------------------------------------------------- */
 
 #error {
@@ -695,7 +886,7 @@ zen-banner {
 
 /* info --------------------------------------------------------------------- */
 
-#info {
+#info, #storage, #network {
 	.info-tiles {
 		grid-template-columns: repeat(auto-fit, minmax(320px, 1fr));
 	}
@@ -1084,6 +1275,207 @@ tr:last-child td {
 	color:				var(--theme_bright);
 }
 
+/* docs --------------------------------------------------------------------- */
+
+.docs-filter {
+	display:				block;
+	width:					100%;
+	max-width:				300px;
+	padding:				8px 12px;
+	font-size:				14px;
+	font-family:			inherit;
+	border:					1px solid var(--theme_g2);
+	border-radius:			6px;
+	background:				var(--theme_bg1);
+	color:					var(--theme_bright);
+	outline:				none;
+	margin-bottom:			12px;
+}
+.docs-filter:focus {
+	border-color:			var(--theme_ln);
+	background:				var(--theme_bg0);
+}
+.docs-filter::placeholder {
+	color:					var(--theme_g1);
+}
+.docs-highlight {
+	background:				var(--theme_highlight);
+	color:					inherit;
+	border-radius:			2px;
+	padding:				0 1px;
+}
+.docs-layout {
+	display:				flex;
+	gap:					24px;
+}
+.docs-sidebar {
+	flex-shrink:			0;
+	width:					200px;
+	border-right:			1px solid var(--theme_g3);
+	padding-right:			16px;
+	display:				flex;
+	flex-direction:			column;
+	gap:					2px;
+	position:				sticky;
+	top:					16px;
+	align-self:				flex-start;
+}
+.docs-sidebar-link {
+	display:				block;
+	padding:				6px 10px;
+	font-size:				13px;
+	color:					var(--theme_g1);
+	text-decoration:		none;
+	border-radius:			4px;
+}
+.docs-sidebar-link:hover {
+	color:					var(--theme_g0);
+	background:				var(--theme_g4);
+}
+.docs-sidebar-link.active {
+	color:					var(--theme_bright);
+	background:				var(--theme_g3);
+	font-weight:			500;
+}
+.docs-content {
+	flex:					1;
+	min-width:				0;
+	font-size:				16px;
+	line-height:			1.5;
+	color:					var(--theme_g0);
+}
+.docs-content h1 {
+	font-size:				24px;
+	font-weight:			600;
+	color:					var(--theme_bright);
+	margin:					0 0 16px 0;
+	padding-bottom:			8px;
+	border-bottom:			1px solid var(--theme_g3);
+	display:				flex;
+	align-items:			center;
+	gap:					8px;
+}
+.docs-source-link {
+	font-size:				14px;
+	opacity:				0.4;
+	transition:				opacity 0.15s;
+	text-decoration:		none;
+}
+.docs-source-link::after {
+	content:				"\2197";
+}
+.docs-source-link:hover,
+.docs-github-link:hover {
+	opacity:				1;
+}
+.docs-github-link {
+	font-size:				14px;
+	opacity:				0.4;
+	transition:				opacity 0.15s;
+	text-decoration:		none;
+}
+.docs-github-link::after {
+	content:				"GH";
+	font-size:				10px;
+	font-weight:			700;
+	letter-spacing:			-0.5px;
+}
+.docs-section {
+	margin-top:				16px;
+}
+.docs-section-title {
+	font-size:				18px;
+	font-weight:			600;
+	color:					var(--theme_bright);
+	cursor:					pointer;
+	list-style:				none;
+	user-select:			none;
+	padding-bottom:			6px;
+	border-bottom:			1px solid var(--theme_g4);
+	margin-bottom:			8px;
+}
+.docs-section-title::-webkit-details-marker {
+	display:				none;
+}
+.docs-section-title::before {
+	content:				"\25B6";
+	display:				inline-block;
+	margin-right:			8px;
+	font-size:				10px;
+	transition:				transform 0.15s;
+	color:					var(--theme_g1);
+}
+.docs-section[open] > .docs-section-title::before {
+	transform:				rotate(90deg);
+}
+.docs-content h2 {
+	font-size:				18px;
+	font-weight:			600;
+	color:					var(--theme_bright);
+	margin:					24px 0 8px 0;
+}
+.docs-content h3 {
+	font-size:				15px;
+	font-weight:			600;
+	color:					var(--theme_bright);
+	margin:					16px 0 6px 0;
+}
+.docs-content p {
+	margin:					0 0 12px 0;
+}
+.docs-content code {
+	background:				var(--theme_bg1);
+	padding:				1px 5px;
+	border-radius:			3px;
+	font-family:			'SF Mono', 'Cascadia Mono', Consolas, 'DejaVu Sans Mono', monospace;
+	font-size:				0.9em;
+	color:					var(--theme_bright);
+}
+.docs-content pre {
+	background:				var(--theme_bg1);
+	padding:				12px 16px;
+	border-radius:			6px;
+	overflow-x:				auto;
+	margin:					0 0 12px 0;
+}
+.docs-content pre code {
+	background:				none;
+	padding:				0;
+}
+.docs-content ul, .docs-content ol {
+	margin:					4px 0 12px 0;
+	padding-left:			24px;
+}
+.docs-content table {
+	border-collapse:		collapse;
+	margin:					8px 0 12px 0;
+	font-size:				13px;
+}
+.docs-content th, .docs-content td {
+	border:					1px solid var(--theme_g3);
+	padding:				4px 10px;
+}
+.docs-content th {
+	background:				var(--theme_bg1);
+	font-weight:			600;
+	color:					var(--theme_bright);
+}
+.docs-content a {
+	color:					var(--theme_ln);
+}
+.docs-mermaid {
+	margin:					12px 0;
+	overflow-x:				auto;
+}
+.docs-mermaid svg {
+	max-width:				100%;
+	height:					auto;
+}
+.docs-loading, .docs-error {
+	color:					var(--theme_g1);
+	font-style:				italic;
+}
+
 /* module action controls --------------------------------------------------- */
 
 .module-state-dot {