fix: get_device_info checked for 'data' attr instead of 'payload'

Event objects use 'payload', not 'data'. This bug was latent because
the cache was always populated during connect — only exposed after
the cache invalidation fix.

Co-Authored-By: Claude Opus 4.6 <noreply@anthropic.com>

app/device_manager.py

@@ -1986,8 +1986,8 @@ class DeviceManager:
 
         try:
             event = self.execute(self.mc.commands.send_appstart())
-            if event and hasattr(event, 'data'):
-                self._self_info = getattr(event, 'payload', {})
+            if event and hasattr(event, 'payload'):
+                self._self_info = event.payload
                 return dict(self._self_info)
         except Exception as e:
             logger.error(f"Failed to get device info: {e}")