Add standalone FastAPI server backend (Phase 3)

Build a complete standalone web server for Immich album change
notifications, independent of Home Assistant. Uses the shared
core library from Phase 1.

Server features:
- FastAPI with async SQLite (SQLModel + aiosqlite)
- Multi-user auth with JWT (admin/user roles, setup wizard)
- CRUD APIs: Immich servers, album trackers, message templates,
  notification targets (Telegram + webhook), user management
- APScheduler background polling per tracker
- Jinja2 template rendering with live preview
- Album browser proxied from Immich API
- Event logging and dashboard status endpoint
- Docker deployment (single container, SQLite in volume)

39 API routes, 14 integration tests passing.

Also adds Phase 6 (Claude AI Telegram bot enhancement) to the
primary plan as an optional future phase.

Co-Authored-By: Claude Opus 4.6 (1M context) <noreply@anthropic.com>

packages/server/src/immich_watcher_server/services/scheduler.py

@@ -0,0 +1,99 @@
+"""Background job scheduler for album polling."""
+
+from __future__ import annotations
+
+import logging
+
+from apscheduler.schedulers.asyncio import AsyncIOScheduler
+from apscheduler.triggers.interval import IntervalTrigger
+from sqlmodel import select
+from sqlmodel.ext.asyncio.session import AsyncSession
+
+from ..database.engine import get_engine
+from ..database.models import AlbumTracker
+from .watcher import check_tracker
+
+_LOGGER = logging.getLogger(__name__)
+
+_scheduler: AsyncIOScheduler | None = None
+
+
+def get_scheduler() -> AsyncIOScheduler:
+    """Get the global scheduler instance."""
+    global _scheduler
+    if _scheduler is None:
+        _scheduler = AsyncIOScheduler()
+    return _scheduler
+
+
+async def start_scheduler() -> None:
+    """Start the scheduler and load all enabled trackers."""
+    scheduler = get_scheduler()
+
+    engine = get_engine()
+    async with AsyncSession(engine) as session:
+        result = await session.exec(
+            select(AlbumTracker).where(AlbumTracker.enabled == True)  # noqa: E712
+        )
+        trackers = result.all()
+
+    for tracker in trackers:
+        _add_tracker_job(scheduler, tracker.id, tracker.scan_interval)
+
+    scheduler.start()
+    _LOGGER.info("Scheduler started with %d tracker jobs", len(trackers))
+
+
+async def stop_scheduler() -> None:
+    """Stop the scheduler."""
+    scheduler = get_scheduler()
+    if scheduler.running:
+        scheduler.shutdown(wait=False)
+        _LOGGER.info("Scheduler stopped")
+
+
+def add_tracker_job(tracker_id: int, scan_interval: int) -> None:
+    """Add or update a scheduler job for a tracker."""
+    scheduler = get_scheduler()
+    _add_tracker_job(scheduler, tracker_id, scan_interval)
+
+
+def remove_tracker_job(tracker_id: int) -> None:
+    """Remove a scheduler job for a tracker."""
+    scheduler = get_scheduler()
+    job_id = f"tracker_{tracker_id}"
+    if scheduler.get_job(job_id):
+        scheduler.remove_job(job_id)
+        _LOGGER.debug("Removed scheduler job for tracker %d", tracker_id)
+
+
+def _add_tracker_job(
+    scheduler: AsyncIOScheduler, tracker_id: int, scan_interval: int
+) -> None:
+    """Add or replace a scheduler job."""
+    job_id = f"tracker_{tracker_id}"
+
+    # Remove existing job if present
+    if scheduler.get_job(job_id):
+        scheduler.remove_job(job_id)
+
+    scheduler.add_job(
+        _run_tracker_check,
+        trigger=IntervalTrigger(seconds=scan_interval),
+        id=job_id,
+        args=[tracker_id],
+        replace_existing=True,
+        max_instances=1,
+    )
+    _LOGGER.debug(
+        "Scheduled tracker %d every %d seconds", tracker_id, scan_interval
+    )
+
+
+async def _run_tracker_check(tracker_id: int) -> None:
+    """Run a single tracker check (called by scheduler)."""
+    try:
+        result = await check_tracker(tracker_id)
+        _LOGGER.debug("Tracker %d check result: %s", tracker_id, result)
+    except Exception:
+        _LOGGER.exception("Error checking tracker %d", tracker_id)