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.

packages/server/tests/test_jwt.py

@@ -0,0 +1,74 @@
+"""JWT encode/decode round-trips."""
+
+from __future__ import annotations
+
+from datetime import datetime, timedelta, timezone
+
+import jwt as pyjwt
+import pytest
+
+from notify_bridge_server.auth.jwt import (
+    ALGORITHM,
+    create_access_token,
+    create_refresh_token,
+    decode_token,
+)
+from notify_bridge_server.config import settings
+
+
+def test_access_token_round_trip() -> None:
+    token = create_access_token(user_id=1, role="admin", token_version=3)
+    payload = decode_token(token)
+    assert payload["sub"] == "1"
+    assert payload["type"] == "access"
+    assert payload["role"] == "admin"
+    assert payload["ver"] == 3
+    assert payload["iss"] == settings.jwt_issuer
+    assert payload["aud"] == settings.jwt_audience
+
+
+def test_refresh_token_round_trip() -> None:
+    token = create_refresh_token(user_id=7, token_version=2)
+    payload = decode_token(token)
+    assert payload["type"] == "refresh"
+    assert payload["sub"] == "7"
+
+
+def test_decode_rejects_wrong_audience() -> None:
+    """A token signed with our key but for a different audience is rejected."""
+    now = datetime.now(timezone.utc)
+    forged = pyjwt.encode(
+        {
+            "iss": settings.jwt_issuer,
+            "aud": "other-service",
+            "sub": "1",
+            "type": "access",
+            "ver": 1,
+            "iat": now,
+            "exp": now + timedelta(minutes=5),
+        },
+        settings.secret_key,
+        algorithm=ALGORITHM,
+    )
+    with pytest.raises(pyjwt.InvalidAudienceError):
+        decode_token(forged)
+
+
+def test_decode_rejects_none_alg() -> None:
+    """An ``alg: none`` token must never be accepted."""
+    now = datetime.now(timezone.utc)
+    forged = pyjwt.encode(
+        {
+            "iss": settings.jwt_issuer,
+            "aud": settings.jwt_audience,
+            "sub": "1",
+            "type": "access",
+            "ver": 1,
+            "iat": now,
+            "exp": now + timedelta(minutes=5),
+        },
+        "",
+        algorithm="none",
+    )
+    with pytest.raises(pyjwt.InvalidAlgorithmError):
+        decode_token(forged)