fix: vendored chattolib start_dm called non-existent rooms.start_dm stub (is start_d_m)

vendor/common/chattolib/client.py

@@ -698,7 +698,7 @@ class ChattoClient:
 
     async def start_dm(self, participant_ids: list[str]) -> Room:
         resp = await self._rpc(
-            self._svc.rooms.start_dm(
+            self._svc.rooms.start_d_m(
                 rooms_pb2.StartDMRequest(participant_ids=participant_ids),
                 headers=self._headers(),
             )