Add localhost web console to BlackbookServer (KPI dashboard + safe actions)

[mayeack]

Why

BlackbookServer was headless — an HTTP API plus a tiny menu-bar popover. There was no way to see operational health at a glance: sync status per device, storage, request errors, record counts, or iMessage-sync stats. This adds a localhost-only web console.

What

• Second NWListener bound to 127.0.0.1:8766 (requiredLocalEndpoint). The Cloudflare tunnel forwards only 8765, so the console is never internet-exposed and needs no password. Reuses the existing receiveRequest/sendResponse plumbing; cancelled in stop()/scheduleRestart(). A loopback remote-endpoint check adds defense-in-depth.
• Routes (no header auth; loopback only): GET / → bundled console.html; GET /api/stats → KPI JSON; POST /api/imessage/backfill + /api/imessage/toggle → safe actions (202/200).
• /api/stats aggregates four sections from existing data: sync health (latest heartbeat per device), backups & storage (count/bytes/per-user), requests (today's access-log status histogram + recent tail), data (per-model fetchCount for all 10 models + iMessage stats).
• console.html — one self-contained dark dashboard (inline CSS+JS, no CDN), polls every 5 s, with Sync Last 30 Days and Toggle iMessage Logging buttons. Auto-bundled by the sources: - BlackbookServer glob.
• Wiring: BackupServer.init gains an imessage: param; ServerStatusModel passes it in; ServerMenuView gets an Open Web Console button.

Security

• Loopback bind + remote-endpoint check ⇒ unreachable from the LAN or the tunnel. Safe actions only — no delete-backup / restart / log-prune.

Test plan

• BlackbookServer builds clean (Debug + Release); console.html bundled in Contents/Resources/.
• GET / → 200 text/html (12049 B); GET /api/stats → full JSON (Contacts 1288, backups 5/3.8 MB, 2 sync devices, 148 reqs today). Verified with curl + strict Python HTTP client.
• Not exposed: LAN-IP:8766 → connection refused; https://sync.libersecretorum.com/api/stats → 401 (hits the 8765 sync server; console route absent). Backfill endpoint → 202.
• 13 Swift Testing tests pass.
• Open via the menu Open Web Console on the server Mac and click through the safe actions.

Deploy note

BlackbookServer is not in TestFlight. After merge, rebuild/reinstall locally (commands in docs/test-scenarios/TEST_SCENARIOS.md). Main Blackbook app is untouched.

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