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, 28 insertions, 4 deletions

diff --git a/src/zenserver/xmake.lua b/src/zenserver/xmake.lua
index aa306190f..c2c81e7aa 100644
--- a/src/zenserver/xmake.lua
+++ b/src/zenserver/xmake.lua
@@ -34,6 +34,7 @@ target("zenserver")
     add_deps("sol2")
     add_packages("http_parser")
     add_packages("json11")
+    add_packages("zlib")
     add_packages("lua")
     add_packages("consul")
     add_packages("minio")
@@ -85,6 +86,7 @@ target("zenserver")
    
     on_load(function(target)
         local html_dir = path.join(os.projectdir(), "src/zenserver/frontend/html")
+        local docs_dir = path.join(os.projectdir(), "docs")
         local zip_dir = path.join(os.projectdir(), get_config("buildir") or "build", "frontend")
         local zip_path = path.join(zip_dir, "html.zip")
 
@@ -92,34 +94,56 @@ target("zenserver")
         local need_update = not os.isfile(zip_path)
         if not need_update then
             local zip_mtime = os.mtime(zip_path)
+            -- Check html sources
             for _, file in ipairs(os.files(path.join(html_dir, "**"))) do
                 if os.mtime(file) > zip_mtime then
                     need_update = true
                     break
                 end
             end
+            -- Check docs sources (bundled as data/ in the zip)
+            if not need_update and os.isdir(docs_dir) then
+                for _, file in ipairs(os.files(path.join(docs_dir, "**"))) do
+                    if os.mtime(file) > zip_mtime then
+                        need_update = true
+                        break
+                    end
+                end
+            end
         end
 
         if need_update then
             print("Regenerating frontend zip...")
-            os.mkdir(zip_dir)
+
+            -- Stage files in a temporary directory so docs/ appears as data/ in the zip
+            local staging_dir = path.join(zip_dir, "staging")
+            os.tryrm(staging_dir)
+            os.mkdir(staging_dir)
+            os.cp(path.join(html_dir, "*"), staging_dir)
+            if os.isdir(docs_dir) then
+                os.cp(docs_dir, path.join(staging_dir, "data"))
+                os.tryrm(path.join(staging_dir, "data", "dev"))
+            end
+
             os.tryrm(zip_path)
 
             import("detect.tools.find_7z")
             local cmd_7z = find_7z()
             if cmd_7z then
-                os.execv(cmd_7z, {"a", "-mx0", "-bso0", zip_path, path.join(html_dir, ".")})
+                os.execv(cmd_7z, {"a", "-bso0", zip_path, path.join(staging_dir, ".")})
             else
                 import("detect.tools.find_zip")
                 local zip_cmd = find_zip()
                 if zip_cmd then
-                    local oldir = os.cd(html_dir)
-                    os.execv(zip_cmd, {"-r", "-0", "-q", zip_path, "."})
+                    local oldir = os.cd(staging_dir)
+                    os.execv(zip_cmd, {"-r", "-q", zip_path, "."})
                     os.cd(oldir)
                 else
                     raise("Unable to find a suitable zip tool (need 7z or zip)")
                 end
             end
+
+            os.tryrm(staging_dir)
         end
     end)