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/src/notify_bridge_server/services/scheduler.py

@@ -85,7 +85,21 @@ def _compute_jitter(interval_seconds: int) -> int:
 def get_scheduler() -> AsyncIOScheduler:
     global _scheduler
     if _scheduler is None:
-        _scheduler = AsyncIOScheduler()
+        # Sensible production defaults applied to every job unless overridden:
+        #   * coalesce — collapse a queue of missed runs into one firing after
+        #     a restart / pause, instead of bursting to catch up.
+        #   * misfire_grace_time — accept firings up to 5 min late without
+        #     dropping them silently.
+        #   * max_instances=1 — never run two copies of the same tracker tick
+        #     concurrently; the scheduler already enforces this on add_job,
+        #     but we also set it as the default for safety.
+        _scheduler = AsyncIOScheduler(
+            job_defaults={
+                "coalesce": True,
+                "misfire_grace_time": 300,
+                "max_instances": 1,
+            },
+        )
     return _scheduler
 
 
@@ -279,21 +293,38 @@ async def _refresh_telegram_chat_titles() -> None:
 
 
 async def _cleanup_old_events() -> None:
-    """Delete EventLog entries older than 90 days."""
+    """Delete EventLog / WebhookPayloadLog / ActionExecution rows older than the
+    configured retention window. A retention of 0 disables the job.
+    """
     from datetime import datetime, timedelta, timezone
 
     from sqlmodel import delete
     from sqlmodel.ext.asyncio.session import AsyncSession
 
+    from ..config import settings
     from ..database.engine import get_engine
-    from ..database.models import EventLog
+    from ..database.models import ActionExecution, EventLog, WebhookPayloadLog
 
-    cutoff = datetime.now(timezone.utc) - timedelta(days=90)
+    days = settings.event_log_retention_days
+    if days <= 0:
+        _LOGGER.debug("Event log retention disabled (days=0); skipping cleanup")
+        return
+
+    cutoff = datetime.now(timezone.utc) - timedelta(days=days)
     engine = get_engine()
     async with AsyncSession(engine) as session:
         await session.exec(delete(EventLog).where(EventLog.created_at < cutoff))
+        await session.exec(
+            delete(WebhookPayloadLog).where(WebhookPayloadLog.created_at < cutoff)
+        )
+        await session.exec(
+            delete(ActionExecution).where(ActionExecution.started_at < cutoff)
+        )
         await session.commit()
-    _LOGGER.info("Cleaned up event log entries older than %s", cutoff.date())
+    _LOGGER.info(
+        "Cleaned event_log / webhook_payload_log / action_execution older than %s",
+        cutoff.date(),
+    )
 
 
 async def _load_tracker_jobs() -> None: