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/main.py

@@ -23,6 +23,7 @@ from .api.targets import router as targets_router
 from .api.users import router as users_router
 from .api.status import router as status_router
 from .api.sync import router as sync_router
+from .api.telegram_bots import router as telegram_bots_router
 from .ai.telegram_webhook import router as telegram_ai_router
 
 logging.basicConfig(
@@ -74,6 +75,7 @@ app.include_router(targets_router)
 app.include_router(users_router)
 app.include_router(status_router)
 app.include_router(sync_router)
+app.include_router(telegram_bots_router)
 app.include_router(telegram_ai_router)
 
 # Serve frontend static files if available