fix: handle /help command directly in Telegram, bypassing ACL check

The /help command was routed through _forward_command → _handle_message
→ is_allowed(), which denied access to users not in the allowFrom list.
Since /help is purely informational, it should be accessible to all
users — similar to how /start already works with its own handler.

Add a dedicated _on_help handler that replies directly without going
through the message bus access control.

Closes #687

nanobot/channels/telegram.py

@@ -146,7 +146,7 @@ class TelegramChannel(BaseChannel):
         # Add command handlers
         self._app.add_handler(CommandHandler("start", self._on_start))
         self._app.add_handler(CommandHandler("new", self._forward_command))
-        self._app.add_handler(CommandHandler("help", self._forward_command))
+        self._app.add_handler(CommandHandler("help", self._on_help))
         
         # Add message handler for text, photos, voice, documents
         self._app.add_handler(
@@ -266,6 +266,20 @@ class TelegramChannel(BaseChannel):
             "Type /help to see available commands."
         )
 
+    async def _on_help(self, update: Update, context: ContextTypes.DEFAULT_TYPE) -> None:
+        """Handle /help command directly, bypassing access control.
+
+        /help is informational and should be accessible to all users,
+        even those not in the allowFrom list.
+        """
+        if not update.message:
+            return
+        await update.message.reply_text(
+            "🐈 nanobot commands:\n"
+            "/new — Start a new conversation\n"
+            "/help — Show available commands"
+        )
+
     @staticmethod
     def _sender_id(user) -> str:
         """Build sender_id with username for allowlist matching."""