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, 75 insertions, 4 deletions

diff --git a/src/zenserver/storage/zenstorageserver.cpp b/src/zenserver/storage/zenstorageserver.cpp
index 68d722f60..de00eb1c2 100644
--- a/src/zenserver/storage/zenstorageserver.cpp
+++ b/src/zenserver/storage/zenstorageserver.cpp
@@ -34,9 +34,11 @@
 #include <zentelemetry/otlptrace.h>
 #include <zenutil/logging.h>
 #include <zenutil/service.h>
+#include <zenutil/sessionsclient.h>
 #include <zenutil/workerpools.h>
 #include <zenutil/zenserverprocess.h>
-#include "../sessions/sessions.h"
+#include "sessions/inprocsessionlogsink.h"
+#include "sessions/sessions.h"
 
 #if ZEN_PLATFORM_WINDOWS
 #	include <zencore/windows.h>
@@ -251,7 +253,22 @@ ZenStorageServer::InitializeServices(const ZenStorageServerConfig& ServerOptions
 
 	{
 		m_SessionsService	  = std::make_unique<SessionsService>();
-		m_HttpSessionsService = std::make_unique<HttpSessionsService>(m_StatusService, m_StatsService, *m_SessionsService);
+		m_HttpSessionsService = std::make_unique<HttpSessionsService>(m_StatusService, m_StatsService, *m_SessionsService, m_IoContext);
+		m_HttpSessionsService->SetSelfSessionId(GetSessionId());
+
+		m_InProcSessionLogSink = logging::SinkPtr(new InProcSessionLogSink(*m_SessionsService));
+		m_InProcSessionLogSink->SetLevel(logging::Info);
+		GetDefaultBroadcastSink()->AddSink(m_InProcSessionLogSink);
+	}
+
+	if (!ServerOptions.SessionsTargetUrl.empty())
+	{
+		m_SessionsClient = std::make_unique<SessionsServiceClient>(SessionsServiceClient::Options{
+			.TargetUrl = ServerOptions.SessionsTargetUrl,
+			.AppName   = "zenserver",
+			.Mode	   = GetServerMode(),
+			.SessionId = GetSessionId(),
+		});
 	}
 
 	if (ServerOptions.BuildStoreConfig.Enabled)
@@ -821,6 +838,17 @@ ZenStorageServer::Run()
 
 	OnReady();
 
+	m_SessionsService->RegisterSession(GetSessionId(), "zenserver", GetServerMode(), Oid::Zero, {});
+
+	if (m_SessionsClient)
+	{
+		(void)m_SessionsClient->Announce();
+		EnqueueSessionAnnounceTimer();
+
+		m_SessionLogSink = m_SessionsClient->CreateLogSink();
+		GetDefaultBroadcastSink()->AddSink(m_SessionLogSink);
+	}
+
 	if (m_IsPowerCycle)
 	{
 		ZEN_INFO("Power cycle mode enabled -- shutting down");
@@ -841,19 +869,48 @@ ZenStorageServer::Cleanup()
 	ZEN_INFO(ZEN_APP_NAME " cleaning up");
 	try
 	{
+		m_SessionAnnounceTimer.cancel();
+
+		// Stop the IO context and join its thread first, before removing sinks.
+		// This ensures no async operations are trying to log through the
+		// broadcast sink while we modify its sink list.
 		m_IoContext.stop();
 		if (m_IoRunner.joinable())
 		{
 			m_IoRunner.join();
 		}
 
-		ShutdownServices();
-
+		// Close the HTTP server before removing sinks. HTTP worker threads
+		// continuously log messages and hold the BroadcastSink shared lock,
+		// which would starve the exclusive lock needed by RemoveSink().
 		if (m_Http)
 		{
 			m_Http->Close();
 		}
 
+		if (m_InProcSessionLogSink)
+		{
+			GetDefaultBroadcastSink()->RemoveSink(m_InProcSessionLogSink);
+			m_InProcSessionLogSink = {};
+		}
+		if (m_SessionLogSink)
+		{
+			GetDefaultBroadcastSink()->RemoveSink(m_SessionLogSink);
+			m_SessionLogSink = {};
+		}
+		if (m_SessionsClient)
+		{
+			(void)m_SessionsClient->Remove();
+			m_SessionsClient.reset();
+		}
+
+		if (m_SessionsService)
+		{
+			m_SessionsService->RemoveSession(GetSessionId());
+		}
+
+		ShutdownServices();
+
 		if (m_JobQueue)
 		{
 			m_JobQueue->Stop();
@@ -938,6 +995,20 @@ ZenStorageServer::CheckStateMarker()
 }
 
 void
+ZenStorageServer::EnqueueSessionAnnounceTimer()
+{
+	m_SessionAnnounceTimer.expires_after(std::chrono::seconds(15));
+	m_SessionAnnounceTimer.async_wait([this](const asio::error_code& Ec) {
+		if (!Ec && m_SessionsClient)
+		{
+			(void)m_SessionsClient->Announce();
+			EnqueueSessionAnnounceTimer();
+		}
+	});
+	EnsureIoRunner();
+}
+
+void
 ZenStorageServer::Flush()
 {
 	ZEN_TRACE_CPU("ZenStorageServer::Flush");