T10: Monitoring, Performance, Documentation & Environment Config — 38 tests, ruff clean, docs OK

- Extended health endpoint: DB+Redis+Storage+Worker checks with degraded status
- Prometheus metrics endpoint: admin-only, text/plain format
- Metrics: http_requests_total, db_pool_connections, arq_jobs_total
- Structured JSON logging (structlog): timestamp, level, method, path, status, duration_ms, tenant_id
- Performance: page_size max 100 enforced (422), streaming CSV export (StreamingResponse)
- Scripts: seed_perf_data.py, check_indexes.py
- Docs: admin-guide.md (Deploy, Backup, Restore, Env-Vars, Troubleshooting), api-overview.md
- README updated: prod setup, API section, env profiles, admin-guide link
- .env.example: added SECRET_KEY, STORAGE_PATH, SMTP_* vars
- 38 new tests, full regression 564/564 pass (0 failures)
- Ruff: all checks passed

app/routes/health.py

@@ -1,13 +1,19 @@
-"""Health check endpoint."""
+"""Health check endpoint — extended with DB, Redis, storage, worker checks."""
 
 from __future__ import annotations
 
 from fastapi import APIRouter
 
+from app.core.monitoring import get_health_status
+
 router = APIRouter(tags=["health"])
 
 
 @router.get("/api/v1/health")
 async def health():
-    """Health check — no auth required."""
-    return {"status": "ok", "version": "1.0.0"}
+    """Health check — no auth required.
+
+    Returns status (healthy/degraded) and individual checks for
+    database, redis, storage, and worker.
+    """
+    return await get_health_status()