feat: production-readiness hardening across security, async, DB, ops

Security
- SSRF: async DNS resolver; allow_redirects=False on all outbound clients;
  matrix homeserver_url validated on create/update/test; update_provider
  and email_bot merge incoming config and reject ***-masked secrets.
- Auth: bcrypt offloaded to asyncio.to_thread; JWT now carries iss/aud +
  leeway and rejects missing claims; setup TOCTOU closed inside a
  transaction; rate limits extended (default 600/min, 10/min on password
  change, 30/min on needs-setup); constant-time login to prevent username
  enumeration.
- Config: rejects known dev secret keys; validates CORS origin schemes,
  port range, token lifetimes.
- Webhook handlers stream-read body with a 1 MiB cap; Discord 429 retries
  bounded (3 attempts, Retry-After capped at 60 s).
- CSP + HSTS added to SecurityHeadersMiddleware.

Async / runtime
- SQLite engine: WAL, synchronous=NORMAL, foreign_keys=ON, busy_timeout,
  pool_pre_ping, dispose on shutdown.
- Lifespan shutdown now stops scheduler before closing HTTP session and
  disposing the engine.
- Shared aiohttp session locked against concurrent first-caller races;
  core NotificationDispatcher accepts and reuses it.
- Storage and scheduled backup writes wrapped in asyncio.to_thread.
- NUT client writes bounded by asyncio.wait_for.
- Telegram poller switched from 3 s short-poll to 30 s interval + 25 s
  long-poll (~10x fewer API calls).

Database
- New performance-indexes migration covers every FK/owner column and
  hot-path composite (notification_tracker(provider_id, enabled);
  event_log(user_id, created_at DESC); webhook_payload_log(provider_id,
  created_at DESC); action_execution(action_id, started_at DESC)).
- New schema_version table for future upgrade gating.
- __system__ placeholder user (id=0) seeded so user_id=0 system defaults
  satisfy the newly enforced FK; filtered out of /auth/needs-setup,
  /api/users, and setup.
- list_notification_trackers rewritten to batched loads (was 1+N+N*M).
- Retention job extended to event_log, webhook_payload_log, and
  action_execution; retention days exposed as a setting.

Scheduler
- AsyncIOScheduler job_defaults: coalesce, misfire_grace_time=300,
  max_instances=1.

Ops
- uvicorn runs with proxy_headers, forwarded_allow_ips,
  timeout_graceful_shutdown; access log suppressed in non-debug.
- FastAPI version string now reads from importlib.metadata.
- New /api/ready endpoint separate from /api/health.
- docker-compose drops the ALLOW_PRIVATE_URLS=1 default, adds mem/cpu/pid
  limits, read_only + tmpfs, cap_drop:ALL, no-new-privileges; healthcheck
  targets /api/ready.
- CI now runs on push/PR with backend pytest, frontend svelte-check +
  build, and a non-push image build; release workflow gated on tests,
  publishes immutable sha-<commit> image tag, adds Trivy scan.

Tests
- New packages/server/tests/ with 29 passing tests: config validation,
  JWT round-trip + aud/alg=none rejection, SSRF scheme and private-range
  enforcement (sync + async), Discord bounded retry, and a lifespan-level
  /api/health + /api/ready smoke check.
- Renamed the misnamed services/test_dispatch.py to manual_dispatch.py so
  pytest never auto-collects production code.

Frontend
- /login now redirects already-authenticated users to /, shows a distinct
  'backend unreachable' banner (en/ru) when /auth/needs-setup fails.

frontend/src/lib/i18n/en.json

@@ -55,7 +55,8 @@
 		"passwordTooShort": "Password must be at least 8 characters",
 		"or": "or",
 		"loginFailed": "Login failed",
-		"setupFailed": "Setup failed"
+		"setupFailed": "Setup failed",
+		"backendUnreachable": "Cannot reach the server. Check that it's running and try again."
 	},
 	"dashboard": {
 		"title": "Dashboard",

frontend/src/lib/i18n/ru.json

@@ -55,7 +55,8 @@
 		"passwordTooShort": "Пароль должен быть не менее 8 символов",
 		"or": "или",
 		"loginFailed": "Ошибка входа",
-		"setupFailed": "Ошибка настройки"
+		"setupFailed": "Ошибка настройки",
+		"backendUnreachable": "Не удалось подключиться к серверу. Убедитесь, что он запущен, и повторите попытку."
 	},
 	"dashboard": {
 		"title": "Главная",

frontend/src/routes/login/+page.svelte

@@ -15,13 +15,32 @@
 	let submitting = $state(false);
 	let mounted = $state(false);
 
+	let backendDown = $state(false);
+
 	onMount(async () => {
 		initTheme();
 		mounted = true;
+		// If the user is already signed in (valid access token in storage),
+		// there is no reason to show them the login form. loadUser() runs in
+		// the root layout; we just check the resolved state after a short tick.
+		const { isAuthenticated } = await import('$lib/api');
+		if (isAuthenticated()) {
+			try {
+				await api('/auth/me');
+				goto('/');
+				return;
+			} catch {
+				// Token was stale; fall through to the login form.
+			}
+		}
 		try {
 			const res = await api<{ needs_setup: boolean }>('/auth/needs-setup');
 			if (res.needs_setup) goto('/setup');
-		} catch { /* ignore */ }
+		} catch {
+			// The backend is unreachable — surface that distinctly so the user
+			// doesn't blame the login form for a network/backend problem.
+			backendDown = true;
+		}
 	});
 
 	async function handleSubmit(e: SubmitEvent) {
@@ -62,7 +81,12 @@
 		<p class="text-sm mt-1" style="color: var(--color-muted-foreground);">{t('auth.signInTitle')}</p>
 	</div>
 
-	{#if error}
+	{#if backendDown}
+		<div class="auth-error animate-fade-slide-in">
+			<MdiIcon name="mdiAlertCircle" size={16} />
+			{t('auth.backendUnreachable')}
+		</div>
+	{:else if error}
 		<div class="auth-error animate-fade-slide-in">
 			<MdiIcon name="mdiAlertCircle" size={16} />
 			{error}