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, 133 insertions, 0 deletions

diff --git a/src/zenserver/storage/admin/admin.cpp b/src/zenserver/storage/admin/admin.cpp
index 6e78a6179..f1c2daea4 100644
--- a/src/zenserver/storage/admin/admin.cpp
+++ b/src/zenserver/storage/admin/admin.cpp
@@ -791,6 +791,139 @@ HttpAdminService::HttpAdminService(GcScheduler&			   Scheduler,
 		},
 		HttpVerb::kPost);
 	m_Router.RegisterRoute(
+		"storage",
+		[this](HttpRouterRequest& Req) {
+			CbObjectWriter Obj;
+
+			// Collect known storage directories
+			struct StorageDir
+			{
+				std::string_view	  Name;
+				std::filesystem::path Path;
+			};
+
+			std::vector<StorageDir>		 Dirs;
+			const std::filesystem::path& DataDir = m_ServerOptions.DataDir;
+			Dirs.push_back({"cache"sv, DataDir / "cache"});
+			Dirs.push_back({"cas"sv, DataDir / "cas"});
+			Dirs.push_back({"projects"sv, DataDir / "projects"});
+			Dirs.push_back({"builds"sv, DataDir / "builds"});
+			Dirs.push_back({"builds_cas"sv, DataDir / "builds_cas"});
+			Dirs.push_back({"obj"sv, DataDir / "obj"});
+
+			// Group directories by volume (identified by total capacity)
+			struct VolumeInfo
+			{
+				DiskSpace					   Space;
+				std::vector<const StorageDir*> Directories;
+			};
+
+			// Use canonical path to identify volumes. Directories on the same volume
+			// will report the same total capacity from DiskSpaceInfo.
+			std::vector<VolumeInfo> Volumes;
+			auto					FindOrAddVolume = [&](DiskSpace Space) -> VolumeInfo& {
+				   for (VolumeInfo& V : Volumes)
+				   {
+					   if (V.Space.Total == Space.Total && V.Space.Free == Space.Free)
+					   {
+						   return V;
+					   }
+				   }
+				   Volumes.push_back({Space, {}});
+				   return Volumes.back();
+			};
+
+			for (StorageDir& Dir : Dirs)
+			{
+				if (!IsDir(Dir.Path))
+				{
+					continue;
+				}
+				DiskSpace Space;
+				if (DiskSpaceInfo(Dir.Path, Space))
+				{
+					FindOrAddVolume(Space).Directories.push_back(&Dir);
+				}
+			}
+
+			Obj.BeginArray("volumes"sv);
+			for (const VolumeInfo& Vol : Volumes)
+			{
+				Obj.BeginObject();
+				Obj << "total"sv << Vol.Space.Total;
+				Obj << "free"sv << Vol.Space.Free;
+				Obj << "used"sv << (Vol.Space.Total - Vol.Space.Free);
+
+				Obj.BeginArray("directories"sv);
+				for (const StorageDir* Dir : Vol.Directories)
+				{
+					Obj.BeginObject();
+					Obj << "name"sv << Dir->Name;
+					Obj << "path"sv << Dir->Path.string();
+
+					DirStats Stats = GetStatsForDirectory(Dir->Path);
+					Obj << "bytes"sv << Stats.ByteCount;
+					Obj << "files"sv << Stats.FileCount;
+					Obj.EndObject();
+				}
+				Obj.EndArray();
+				Obj.EndObject();
+			}
+			Obj.EndArray();
+
+			Req.ServerRequest().WriteResponse(HttpResponseCode::OK, Obj.Save());
+		},
+		HttpVerb::kGet);
+
+	m_Router.RegisterRoute(
+		"gclog",
+		[this](HttpRouterRequest& Req) {
+			const GcSchedulerState		State = m_GcScheduler.GetState();
+			const std::filesystem::path Path  = State.Config.RootDirectory / "gc.log";
+
+			CbObjectWriter Response;
+			Response.BeginArray("entries"sv);
+
+			try
+			{
+				if (IsFile(Path))
+				{
+					IoBuffer FileData = ReadFile(Path).Flatten();
+
+					// The log file contains concatenated named CBO object fields.
+					// Each field is a complete entry: [type+name header][object payload].
+					// We wrap each one in a CbObject and add it to the response array.
+					const uint8_t* Ptr = static_cast<const uint8_t*>(FileData.GetData());
+					const uint8_t* End = Ptr + FileData.GetSize();
+
+					while (Ptr < End)
+					{
+						CbFieldView Field(Ptr);
+						uint64_t	FieldSize = Field.GetSize();
+						if (FieldSize == 0 || Ptr + FieldSize > End)
+						{
+							break;
+						}
+
+						// Wrap the named field as an object and add it
+						CbObjectView ObjView = Field.AsObjectView();
+						CbObject	 Entry	 = CbObject::Clone(ObjView);
+						Response.AddObject(Entry);
+						Ptr += FieldSize;
+					}
+				}
+			}
+			catch (const std::exception& Ex)
+			{
+				ZEN_WARN("failed to read gc log '{}': {}", Path, Ex.what());
+			}
+
+			Response.EndArray();
+			Req.ServerRequest().WriteResponse(HttpResponseCode::OK, Response.Save());
+		},
+		HttpVerb::kGet);
+
+	m_Router.RegisterRoute(
 		"flush",
 		[this](HttpRouterRequest& Req) {
 			HttpServerRequest& HttpReq = Req.ServerRequest();