feat(telegram): add 'none' listener mode for bots

Introduce a third update_mode option alongside polling/webhook. 'none'
disables both polling and webhook delivery — useful when another instance
owns the listener or when the bot is send-only. Switching into 'none' now
unschedules polling and unregisters any active webhook so Telegram stops
delivering updates.

New bots default to 'none' (safer when multiple bridges share a token).
Existing bots upgraded from a pre-update_mode schema keep 'polling' so
their behavior is unchanged.

packages/server/src/notify_bridge_server/api/telegram_bots.py

@@ -86,6 +86,11 @@ async def update_bot(
         bot.icon = body.icon
     # Handle mode switching
     if body.update_mode is not None and body.update_mode != bot.update_mode:
+        if body.update_mode not in ("none", "polling", "webhook"):
+            raise HTTPException(
+                status_code=400,
+                detail=f"Invalid update_mode: {body.update_mode!r}. Must be 'none', 'polling', or 'webhook'.",
+            )
         if body.update_mode == "webhook":
             # Validate and register webhook BEFORE stopping polling
             base_url = await get_setting(session, "external_url")
@@ -108,6 +113,12 @@ async def update_bot(
             # Switching to polling: unregister webhook, start polling
             await unregister_webhook(bot.token)
             schedule_bot_polling(bot.id)
+        elif body.update_mode == "none":
+            # Disable listener: stop polling and clear any webhook so Telegram
+            # stops delivering updates. This makes the bot send-only, which is
+            # safe when another instance owns the listener.
+            unschedule_bot_polling(bot.id)
+            await unregister_webhook(bot.token)
         bot.update_mode = body.update_mode
 
     session.add(bot)
@@ -406,7 +417,7 @@ def _bot_response(b: TelegramBot) -> dict:
         "bot_username": b.bot_username,
         "bot_id": b.bot_id,
         "webhook_path_id": b.webhook_path_id,
-        "update_mode": b.update_mode or "polling",
+        "update_mode": b.update_mode or "none",
         "token_preview": f"{b.token[:8]}...{b.token[-4:]}" if len(b.token) > 12 else "***",
         "created_at": b.created_at.isoformat(),
     }