Add service health checks and dynamic Apps page

Backend polls each registered service's /health endpoint every 30 s via a
background asyncio task. GET /api/services exposes the live status snapshot.
The Apps page now renders from this endpoint — showing "Unavailable" (dimmed,
non-clickable) when a service is registered but its container is unreachable.

Co-Authored-By: Claude Sonnet 4.6 <noreply@anthropic.com>

backend/STATUS.md

@@ -40,6 +40,14 @@ JWT signing uses a 4096-bit RSA key pair (`RS256`). Keys are generated by `scrip
 | `GET` | `/api/admin/users` | List all users (admin only) |
 | `PATCH` | `/api/admin/users/{id}` | Update user (role, active flag) |
 
+### Services (`/api/services`)
+
+| Method | Path | Description |
+|--------|------|-------------|
+| `GET` | `/api/services` | Returns health status of all registered feature services |
+
+A background task (`service_health.py`) polls each service's `/health` endpoint every 30 s and stores the result in memory. The first check runs immediately on startup. Any authenticated user may call `GET /api/services`; the frontend uses it to drive app card visibility.
+
 ### Settings (`/api/settings`)
 
 | Method | Path | Description |
@@ -80,11 +88,11 @@ Browser (port 5173 dev / 80 prod)
             │
             └── /api/*  →  backend:8000  (FastAPI)
                                 │
-                    ┌───────────┼────────────┐
-                 /auth       /settings    /documents/*
-                 /users       (JSON        │
-                 /admin        volume)     └── proxy → doc-service:8001
-                 /profile
+                    ┌───────────┼────────────┬──────────────┐
+                 /auth       /settings    /documents/*   /services
+                 /users       (JSON        │              │
+                 /admin        volume)     └── proxy →   health-check loop
+                 /profile                  doc-service:8001  (30s poll)
 ```
 
 ---