Phase 9: Telegram bot management with chat discovery

New entity + API:
- TelegramBot model (name, token, bot_username, bot_id)
- CRUD at /api/telegram-bots with token validation via getMe
- GET /{id}/chats: discover active chats via getUpdates
- GET /{id}/token: retrieve full token (for target config)

Frontend:
- /telegram-bots page: register bots, view discovered chats
  per bot (expandable), refresh on demand
- Targets page: select from registered bots (dropdown) instead
  of raw token input. Chat selector shows discovered chats
  when bot is selected, falls back to manual input.
  Bot token resolved server-side on save.

Nav icon uses monochrome symbol for consistency.

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

packages/server/src/immich_watcher_server/database/__init__.py

@@ -7,6 +7,7 @@ from .models import (
     EventLog,
     ImmichServer,
     NotificationTarget,
+    TelegramBot,
     TemplateConfig,
     TrackingConfig,
     User,

packages/server/src/immich_watcher_server/database/models.py

@@ -36,6 +36,20 @@ class ImmichServer(SQLModel, table=True):
     created_at: datetime = Field(default_factory=_utcnow)
 
 
+class TelegramBot(SQLModel, table=True):
+    """Registered Telegram bot."""
+
+    __tablename__ = "telegram_bot"
+
+    id: int | None = Field(default=None, primary_key=True)
+    user_id: int = Field(foreign_key="user.id")
+    name: str  # User-given display name
+    token: str  # Bot API token
+    bot_username: str = Field(default="")  # @username from getMe
+    bot_id: int = Field(default=0)  # Numeric bot ID from getMe
+    created_at: datetime = Field(default_factory=_utcnow)
+
+
 class TrackingConfig(SQLModel, table=True):
     """Tracking configuration: what events/assets to react to and scheduled modes."""