fix: raise error when Telegram bot not running instead of silently dropping messages

When the outbound dispatcher processes recovery notifications before the
Telegram bot is fully started, the send() method silently returned, causing
the notification to be lost. Now it raises RuntimeError so _send_with_retry
will retry until the bot is ready.

nanobot/channels/telegram/runtime.py

@@ -729,7 +729,7 @@ class TelegramChannel(BaseChannel):
         """Send a message through Telegram."""
         if not self._app:
             self.logger.warning("bot not running")
-            return
+            raise RuntimeError("Telegram bot is not running")
 
         progress_event = msg.event if isinstance(msg.event, ProgressEvent) else None