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()`

3 files changed, 104 insertions, 8 deletions

diff --git a/src/zenserver/frontend/html/util/compactbinary.js b/src/zenserver/frontend/html/util/compactbinary.js
index 415fa4be8..270c96a2f 100644
--- a/src/zenserver/frontend/html/util/compactbinary.js
+++ b/src/zenserver/frontend/html/util/compactbinary.js
@@ -369,6 +369,14 @@ CbObjectView.prototype[Symbol.iterator] = function()
 ////////////////////////////////////////////////////////////////////////////////
 CbObjectView.prototype.to_js_object = function()
 {
+	const TicksPerMs = 10000;
+	const UnixEpochTicks = 621355968000000000n;  // .NET ticks at 1970-01-01
+
+	const readTicks = function(data) {
+		const dv = new DataView(data.buffer, data.byteOffset, 8);
+		return dv.getBigInt64(0, false);
+	};
+
 	const impl = function(node)
 	{
 		if (node.is_object())
@@ -388,9 +396,40 @@ CbObjectView.prototype.to_js_object = function()
 		}
 
 		if (node.is_string())	return node.as_value();
-		if (node.is_integer())	return node.as_value();
 		if (node.is_float())	return node.as_value();
 
+		if (node.is_integer())
+		{
+			const v = node.as_value();
+			if (v >= -9007199254740991n && v <= 9007199254740991n)
+				return Number(v);
+			return v;
+		}
+
+		const type = CbFieldTypeOps.get_type(node.get_type());
+
+		if (type == CbFieldType.DateTime)
+		{
+			const ticks = readTicks(node.as_value());
+			const unixMs = Number((ticks - UnixEpochTicks) / BigInt(TicksPerMs));
+			return new Date(unixMs).toISOString();
+		}
+
+		if (type == CbFieldType.TimeSpan)
+		{
+			const ticks = readTicks(node.as_value());
+			const absTicks = ticks < 0n ? -ticks : ticks;
+			const totalMs = Number(absTicks / BigInt(TicksPerMs));
+			const ms = totalMs % 1000;
+			const totalSec = Math.floor(totalMs / 1000);
+			const sec = totalSec % 60;
+			const totalMin = Math.floor(totalSec / 60);
+			const min = totalMin % 60;
+			const hours = Math.floor(totalMin / 60);
+			const sign = ticks < 0n ? "-" : "";
+			return `${sign}${hours}:${String(min).padStart(2, "0")}:${String(sec).padStart(2, "0")}.${String(ms).padStart(3, "0")}0000`;
+		}
+
 		var ret = node.as_value();
 		if (ret instanceof Uint8Array)
 		{
diff --git a/src/zenserver/frontend/html/util/friendly.js b/src/zenserver/frontend/html/util/friendly.js
index 5d4586165..f400bbce0 100644
--- a/src/zenserver/frontend/html/util/friendly.js
+++ b/src/zenserver/frontend/html/util/friendly.js
@@ -30,6 +30,59 @@ export class Friendly
 		return Friendly.sep(v * 1000000000, 0) + " ns";
 	}
 
+	/** Format a .NET-style TimeSpan string (e.g. "0:05:23.4560000") as a human-readable duration. */
+	static timespan(value)
+	{
+		if (typeof value === "number")
+		{
+			return Friendly._formatDurationMs(value);
+		}
+
+		const str = String(value);
+		const match = str.match(/^[+-]?(?:(\d+)\.)?(\d+):(\d+):(\d+)(?:\.(\d+))?$/);
+		if (!match)
+		{
+			return str;
+		}
+
+		const days = parseInt(match[1] || "0", 10);
+		const hours = parseInt(match[2], 10);
+		const minutes = parseInt(match[3], 10);
+		const seconds = parseInt(match[4], 10);
+		const frac = match[5] ? parseInt(match[5].substring(0, 3).padEnd(3, "0"), 10) : 0;
+		const totalMs = ((days * 86400 + hours * 3600 + minutes * 60 + seconds) * 1000) + frac;
+
+		return Friendly._formatDurationMs(totalMs);
+	}
+
+	static _formatDurationMs(ms)
+	{
+		const seconds = Math.floor(ms / 1000);
+		const minutes = Math.floor(seconds / 60);
+		const hours = Math.floor(minutes / 60);
+		const days = Math.floor(hours / 24);
+
+		if (days > 0)	return `${days}d ${hours % 24}h ${minutes % 60}m`;
+		if (hours > 0)	return `${hours}h ${minutes % 60}m`;
+		if (minutes > 0) return `${minutes}m ${seconds % 60}s`;
+		if (seconds > 0) return `${seconds}.${String(ms % 1000).padStart(3, "0")}s`;
+		return `${ms}ms`;
+	}
+
+	/** Format an ISO / .NET datetime string as a friendly local date+time. */
+	static datetime(value)
+	{
+		const d = new Date(value);
+		if (isNaN(d.getTime()))
+		{
+			return String(value);
+		}
+		return d.toLocaleString(undefined, {
+			year: "numeric", month: "short", day: "numeric",
+			hour: "2-digit", minute: "2-digit", second: "2-digit",
+		});
+	}
+
 	static bytes(x)
 	{
 		const v = BigInt(Math.trunc(Number(x)));
diff --git a/src/zenserver/frontend/html/util/widgets.js b/src/zenserver/frontend/html/util/widgets.js
index 2964f92f2..17bd2fde7 100644
--- a/src/zenserver/frontend/html/util/widgets.js
+++ b/src/zenserver/frontend/html/util/widgets.js
@@ -243,7 +243,7 @@ export class Table extends Widget
 		var row = this._add_row(args);
 		this._rows.push(row);
 
-		if ((this._flags & Table.Flag_AlignNumeric) && this._rows.length === 1)
+		if (this._flags & Table.Flag_AlignNumeric)
 		{
 			this._align_header();
 		}
@@ -253,19 +253,23 @@ export class Table extends Widget
 
 	_align_header()
 	{
-		const first_row = this._rows[0];
-		if (!first_row)
+		if (this._rows.length === 0)
 		{
 			return;
 		}
 		const header_elem = this._element.firstElementChild;
 		const header_cells = header_elem.children;
-		const data_cells = first_row.inner().children;
-		for (let i = 0; i < data_cells.length && i < header_cells.length; i++)
+
+		// A column is numeric if any data row has right-aligned content in it.
+		for (const row of this._rows)
 		{
-			if (data_cells[i].style.textAlign === "right")
+			const data_cells = row.inner().children;
+			for (let i = 0; i < data_cells.length && i < header_cells.length; i++)
 			{
-				header_cells[i].style.textAlign = "right";
+				if (data_cells[i].style.textAlign === "right")
+				{
+					header_cells[i].style.textAlign = "right";
+				}
 			}
 		}
 	}