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/api/users.py

@@ -1,5 +1,6 @@
 """User management API routes (admin only)."""
 
+import asyncio
 import logging
 
 from fastapi import APIRouter, Depends, HTTPException, status
@@ -14,6 +15,15 @@ from ..auth.dependencies import require_admin
 from ..database.engine import get_session
 from ..database.models import User
 
+
+async def _hash_password(password: str) -> str:
+    """Run bcrypt off the event loop. Matches the helper in auth/routes.py."""
+
+    def _work() -> str:
+        return bcrypt.hashpw(password.encode(), bcrypt.gensalt()).decode()
+
+    return await asyncio.to_thread(_work)
+
 _LOGGER = logging.getLogger(__name__)
 
 router = APIRouter(prefix="/api/users", tags=["users"])
@@ -36,8 +46,12 @@ async def list_users(
     admin: User = Depends(require_admin),
     session: AsyncSession = Depends(get_session),
 ):
-    """List all users (admin only)."""
-    result = await session.exec(select(User))
+    """List all users (admin only).
+
+    Excludes the internal ``__system__`` placeholder (id=0) used as the
+    owner of default templates/configs — it is never a real account.
+    """
+    result = await session.exec(select(User).where(User.id != 0))
     return [
         {"id": u.id, "username": u.username, "role": u.role, "created_at": u.created_at.isoformat()}
         for u in result.all()
@@ -61,7 +75,7 @@ async def create_user(
 
     user = User(
         username=body.username,
-        hashed_password=bcrypt.hashpw(body.password.encode(), bcrypt.gensalt()).decode(),
+        hashed_password=await _hash_password(body.password),
         role=body.role if body.role in ("admin", "user") else "user",
     )
     session.add(user)
@@ -162,7 +176,7 @@ async def reset_user_password(
         raise HTTPException(status_code=404, detail="User not found")
     if len(body.new_password) < 8:
         raise HTTPException(status_code=400, detail="Password must be at least 8 characters")
-    user.hashed_password = bcrypt.hashpw(body.new_password.encode(), bcrypt.gensalt()).decode()
+    user.hashed_password = await _hash_password(body.new_password)
     # Invalidate all prior JWTs issued for this user — matches the self-serve
     # password-change path in auth/routes.py.
     user.token_version = (user.token_version or 1) + 1