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/notifier.py

@@ -0,0 +1,128 @@
+"""Notification dispatch service."""
+
+from __future__ import annotations
+
+import logging
+from typing import Any
+
+import aiohttp
+import jinja2
+
+from immich_watcher_core.telegram.client import TelegramClient
+
+from ..database.models import MessageTemplate, NotificationTarget
+from ..webhook.client import WebhookClient
+
+_LOGGER = logging.getLogger(__name__)
+
+# Default template used when no custom template is configured
+DEFAULT_TEMPLATE = (
+    "{{ added_count }} new item(s) added to album \"{{ album_name }}\"."
+    "{% if people %}\nPeople: {{ people | join(', ') }}{% endif %}"
+)
+
+
+def render_template(template_body: str, context: dict[str, Any]) -> str:
+    """Render a Jinja2 template with the given context."""
+    env = jinja2.Environment(autoescape=False)
+    tmpl = env.from_string(template_body)
+    return tmpl.render(**context)
+
+
+async def send_notification(
+    target: NotificationTarget,
+    event_data: dict[str, Any],
+    template: MessageTemplate | None = None,
+) -> dict[str, Any]:
+    """Send a notification to a target using event data.
+
+    Args:
+        target: Notification destination (telegram or webhook)
+        event_data: Album change event data (album_name, added_count, etc.)
+        template: Optional message template (uses default if None)
+    """
+    template_body = template.body if template else DEFAULT_TEMPLATE
+    try:
+        message = render_template(template_body, event_data)
+    except jinja2.TemplateError as e:
+        _LOGGER.error("Template rendering failed: %s", e)
+        message = f"Album changed: {event_data.get('album_name', 'unknown')}"
+
+    if target.type == "telegram":
+        return await _send_telegram(target, message, event_data)
+    elif target.type == "webhook":
+        return await _send_webhook(target, message, event_data)
+    else:
+        return {"success": False, "error": f"Unknown target type: {target.type}"}
+
+
+async def send_test_notification(target: NotificationTarget) -> dict[str, Any]:
+    """Send a test notification to verify target configuration."""
+    test_data = {
+        "album_name": "Test Album",
+        "added_count": 1,
+        "removed_count": 0,
+        "change_type": "assets_added",
+        "people": [],
+        "added_assets": [],
+    }
+
+    if target.type == "telegram":
+        return await _send_telegram(
+            target, "Test notification from Immich Watcher", test_data
+        )
+    elif target.type == "webhook":
+        return await _send_webhook(
+            target, "Test notification from Immich Watcher", test_data
+        )
+    return {"success": False, "error": f"Unknown target type: {target.type}"}
+
+
+async def _send_telegram(
+    target: NotificationTarget, message: str, event_data: dict[str, Any]
+) -> dict[str, Any]:
+    """Send notification via Telegram."""
+    config = target.config
+    bot_token = config.get("bot_token")
+    chat_id = config.get("chat_id")
+
+    if not bot_token or not chat_id:
+        return {"success": False, "error": "Missing bot_token or chat_id in target config"}
+
+    async with aiohttp.ClientSession() as session:
+        client = TelegramClient(session, bot_token)
+
+        # Build assets list from event data for media sending
+        assets = []
+        for asset in event_data.get("added_assets", []):
+            url = asset.get("download_url") or asset.get("url")
+            if url:
+                asset_type = "video" if asset.get("type") == "VIDEO" else "photo"
+                assets.append({"url": url, "type": asset_type})
+
+        return await client.send_notification(
+            chat_id=str(chat_id),
+            caption=message,
+            assets=assets if assets else None,
+        )
+
+
+async def _send_webhook(
+    target: NotificationTarget, message: str, event_data: dict[str, Any]
+) -> dict[str, Any]:
+    """Send notification via webhook."""
+    config = target.config
+    url = config.get("url")
+    headers = config.get("headers", {})
+
+    if not url:
+        return {"success": False, "error": "Missing url in target config"}
+
+    payload = {
+        "message": message,
+        "event": event_data,
+    }
+
+    async with aiohttp.ClientSession() as session:
+        client = WebhookClient(session, url, headers)
+        return await client.send(payload)