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, 377 insertions, 0 deletions

diff --git a/src/zenutil/sessionsclient.cpp b/src/zenutil/sessionsclient.cpp
new file mode 100644
index 000000000..c62cc4099
--- /dev/null
+++ b/src/zenutil/sessionsclient.cpp
@@ -0,0 +1,377 @@
+// Copyright Epic Games, Inc. All Rights Reserved.
+
+#include <zenutil/sessionsclient.h>
+
+#include <zencore/blockingqueue.h>
+#include <zencore/compactbinarybuilder.h>
+#include <zencore/fmtutils.h>
+#include <zencore/iobuffer.h>
+#include <zencore/logging/logmsg.h>
+#include <zencore/thread.h>
+#include <zenhttp/httpclient.h>
+
+#include <thread>
+#include <vector>
+
+ZEN_THIRD_PARTY_INCLUDES_START
+#include <fmt/format.h>
+ZEN_THIRD_PARTY_INCLUDES_END
+
+namespace zen {
+
+//////////////////////////////////////////////////////////////////////////
+//
+// SessionLogSink — batching log sink that forwards to /sessions/{id}/log
+//
+
+static const char*
+LogLevelToString(logging::LogLevel Level)
+{
+	switch (Level)
+	{
+		case logging::Trace:
+			return "trace";
+		case logging::Debug:
+			return "debug";
+		case logging::Info:
+			return "info";
+		case logging::Warn:
+			return "warn";
+		case logging::Err:
+			return "error";
+		case logging::Critical:
+			return "critical";
+		default:
+			return "info";
+	}
+}
+
+struct BufferedLogEntry
+{
+	enum class Type : uint8_t
+	{
+		Log,
+		Flush,
+		Shutdown
+	};
+
+	Type		Type = Type::Log;
+	std::string Level;
+	std::string Message;
+};
+
+class SessionLogSink final : public logging::Sink
+{
+public:
+	SessionLogSink(std::string TargetUrl, std::string LogPath) : m_LogPath(std::move(LogPath))
+	{
+		HttpClientSettings Settings;
+		Settings.ConnectTimeout = std::chrono::milliseconds(3000);
+		m_Http					= std::make_unique<HttpClient>(std::move(TargetUrl), Settings);
+
+		SetLevel(logging::Info);
+
+		m_WorkerThread = std::thread([this]() {
+			zen::SetCurrentThreadName("SessionLog");
+			WorkerLoop();
+		});
+	}
+
+	~SessionLogSink() override
+	{
+		BufferedLogEntry ShutdownMsg;
+		ShutdownMsg.Type = BufferedLogEntry::Type::Shutdown;
+		m_Queue.Enqueue(std::move(ShutdownMsg));
+
+		if (m_WorkerThread.joinable())
+		{
+			m_WorkerThread.join();
+		}
+	}
+
+	void Log(const logging::LogMessage& Msg) override
+	{
+		BufferedLogEntry Entry;
+		Entry.Type	  = BufferedLogEntry::Type::Log;
+		Entry.Level	  = LogLevelToString(Msg.GetLevel());
+		Entry.Message = std::string(Msg.GetPayload());
+		m_Queue.Enqueue(std::move(Entry));
+	}
+
+	void Flush() override
+	{
+		// Best-effort: enqueue a flush marker so the worker sends any pending entries
+		BufferedLogEntry FlushMsg;
+		FlushMsg.Type = BufferedLogEntry::Type::Flush;
+		m_Queue.Enqueue(std::move(FlushMsg));
+	}
+
+	void SetFormatter(std::unique_ptr<logging::Formatter> /*InFormatter*/) override
+	{
+		// No formatting needed — we send raw message text
+	}
+
+private:
+	static constexpr size_t BatchSize = 50;
+
+	void WorkerLoop()
+	{
+		std::vector<BufferedLogEntry> Batch;
+		Batch.reserve(BatchSize);
+
+		BufferedLogEntry Msg;
+		while (m_Queue.WaitAndDequeue(Msg))
+		{
+			if (Msg.Type == BufferedLogEntry::Type::Shutdown)
+			{
+				// Drain remaining log entries
+				BufferedLogEntry Remaining;
+				while (m_Queue.WaitAndDequeue(Remaining))
+				{
+					if (Remaining.Type == BufferedLogEntry::Type::Log)
+					{
+						Batch.push_back(std::move(Remaining));
+					}
+				}
+				if (!Batch.empty())
+				{
+					SendBatch(Batch);
+				}
+				return;
+			}
+
+			if (Msg.Type == BufferedLogEntry::Type::Flush)
+			{
+				if (!Batch.empty())
+				{
+					SendBatch(Batch);
+					Batch.clear();
+				}
+				continue;
+			}
+
+			// Log entry
+			Batch.push_back(std::move(Msg));
+
+			if (Batch.size() >= BatchSize)
+			{
+				SendBatch(Batch);
+				Batch.clear();
+			}
+			else
+			{
+				// Drain any additional queued entries without blocking
+				while (Batch.size() < BatchSize && m_Queue.Size() > 0)
+				{
+					BufferedLogEntry Extra;
+					if (m_Queue.WaitAndDequeue(Extra))
+					{
+						if (Extra.Type == BufferedLogEntry::Type::Shutdown)
+						{
+							if (!Batch.empty())
+							{
+								SendBatch(Batch);
+							}
+							// Drain remaining
+							while (m_Queue.WaitAndDequeue(Extra))
+							{
+								if (Extra.Type == BufferedLogEntry::Type::Log)
+								{
+									Batch.push_back(std::move(Extra));
+								}
+							}
+							if (!Batch.empty())
+							{
+								SendBatch(Batch);
+							}
+							return;
+						}
+						if (Extra.Type == BufferedLogEntry::Type::Log)
+						{
+							Batch.push_back(std::move(Extra));
+						}
+						else if (Extra.Type == BufferedLogEntry::Type::Flush)
+						{
+							break;
+						}
+					}
+				}
+
+				if (!Batch.empty())
+				{
+					SendBatch(Batch);
+					Batch.clear();
+				}
+			}
+		}
+	}
+
+	void SendBatch(const std::vector<BufferedLogEntry>& Batch)
+	{
+		try
+		{
+			CbObjectWriter Writer;
+			Writer.BeginArray("entries");
+			for (const BufferedLogEntry& Entry : Batch)
+			{
+				Writer.BeginObject();
+				Writer << "level" << Entry.Level;
+				Writer << "message" << Entry.Message;
+				Writer.EndObject();
+			}
+			Writer.EndArray();
+
+			HttpClient::Response Result = m_Http->Post(m_LogPath, Writer.Save());
+			(void)Result;  // Best-effort
+		}
+		catch (const std::exception&)
+		{
+			// Best-effort — silently discard on failure
+		}
+	}
+
+	std::string						m_LogPath;
+	std::unique_ptr<HttpClient>		m_Http;
+	BlockingQueue<BufferedLogEntry> m_Queue;
+	std::thread						m_WorkerThread;
+};
+
+SessionsServiceClient::SessionsServiceClient(Options Opts)
+: m_Log(logging::Get("sessionsclient"))
+, m_Options(std::move(Opts))
+, m_SessionPath(fmt::format("sessions/{}", m_Options.SessionId))
+{
+	HttpClientSettings Settings;
+	Settings.ConnectTimeout = std::chrono::milliseconds(3000);
+	m_Http					= std::make_unique<HttpClient>(m_Options.TargetUrl, Settings);
+}
+
+SessionsServiceClient::~SessionsServiceClient() = default;
+
+CbObject
+SessionsServiceClient::BuildRequestBody(CbObjectView Metadata) const
+{
+	CbObjectWriter Writer;
+	Writer << "appname" << m_Options.AppName;
+	if (!m_Options.Mode.empty())
+	{
+		Writer << "mode" << m_Options.Mode;
+	}
+	if (m_Options.JobId != Oid::Zero)
+	{
+		Writer << "jobid" << m_Options.JobId;
+	}
+	if (Metadata.GetSize() > 0)
+	{
+		Writer.AddObject("metadata", Metadata);
+	}
+	return Writer.Save();
+}
+
+bool
+SessionsServiceClient::Announce(CbObjectView Metadata)
+{
+	try
+	{
+		CbObject Body = BuildRequestBody(Metadata);
+
+		HttpClient::Response Result = m_Http->Post(m_SessionPath, std::move(Body));
+
+		if (Result.Error)
+		{
+			ZEN_WARN("sessions announce failed for '{}': HTTP error {} - {}",
+					 m_Options.TargetUrl,
+					 static_cast<int>(Result.Error->ErrorCode),
+					 Result.Error->ErrorMessage);
+			return false;
+		}
+		if (!IsHttpOk(Result.StatusCode))
+		{
+			ZEN_WARN("sessions announce failed for '{}': HTTP status {}", m_Options.TargetUrl, static_cast<int>(Result.StatusCode));
+			return false;
+		}
+
+		ZEN_INFO("session announced to '{}'", m_Options.TargetUrl);
+		return true;
+	}
+	catch (const std::exception& Ex)
+	{
+		ZEN_WARN("sessions announce failed for '{}': {}", m_Options.TargetUrl, Ex.what());
+		return false;
+	}
+}
+
+bool
+SessionsServiceClient::UpdateMetadata(CbObjectView Metadata)
+{
+	try
+	{
+		CbObject Body = BuildRequestBody(Metadata);
+
+		MemoryView View	   = Body.GetView();
+		IoBuffer   Payload = IoBufferBuilder::MakeCloneFromMemory(View, ZenContentType::kCbObject);
+
+		HttpClient::Response Result = m_Http->Put(m_SessionPath, Payload);
+
+		if (Result.Error)
+		{
+			ZEN_WARN("sessions update failed for '{}': HTTP error {} - {}",
+					 m_Options.TargetUrl,
+					 static_cast<int>(Result.Error->ErrorCode),
+					 Result.Error->ErrorMessage);
+			return false;
+		}
+		if (!IsHttpOk(Result.StatusCode))
+		{
+			ZEN_WARN("sessions update failed for '{}': HTTP status {}", m_Options.TargetUrl, static_cast<int>(Result.StatusCode));
+			return false;
+		}
+
+		return true;
+	}
+	catch (const std::exception& Ex)
+	{
+		ZEN_WARN("sessions update failed for '{}': {}", m_Options.TargetUrl, Ex.what());
+		return false;
+	}
+}
+
+bool
+SessionsServiceClient::Remove()
+{
+	try
+	{
+		HttpClient::Response Result = m_Http->Delete(m_SessionPath);
+
+		if (Result.Error)
+		{
+			ZEN_WARN("sessions remove failed for '{}': HTTP error {} - {}",
+					 m_Options.TargetUrl,
+					 static_cast<int>(Result.Error->ErrorCode),
+					 Result.Error->ErrorMessage);
+			return false;
+		}
+		if (!IsHttpOk(Result.StatusCode))
+		{
+			ZEN_WARN("sessions remove failed for '{}': HTTP status {}", m_Options.TargetUrl, static_cast<int>(Result.StatusCode));
+			return false;
+		}
+
+		ZEN_INFO("session removed from '{}'", m_Options.TargetUrl);
+		return true;
+	}
+	catch (const std::exception& Ex)
+	{
+		ZEN_WARN("sessions remove failed for '{}': {}", m_Options.TargetUrl, Ex.what());
+		return false;
+	}
+}
+
+logging::SinkPtr
+SessionsServiceClient::CreateLogSink()
+{
+	std::string LogPath = m_SessionPath + "/log";
+	return Ref(new SessionLogSink(m_Options.TargetUrl, std::move(LogPath)));
+}
+
+}  // namespace zen