feat(max-bot): implement mock-based message flow with WIP file queue

- MAX API integration (long polling)
- MockPlatformClient for agent simulation
- File download & workspace storage
- Basic commands: /help, /start
- Attachment queue: add works, list/remove need testing

[WIP: attachment queue commands]
[MOCK-ONLY: requires real agent for production]

adapter/max/converter.py

@@ -47,6 +47,8 @@ def incoming_from_text_commands(
 
     raw = stripped[1:]
     parts = raw.split(maxsplit=1)
+    if not parts:
+        return None 
     name = (parts[0] or "").lower()
     tail = parts[1] if len(parts) > 1 else ""