feat(matrix): implement !reset via new platform_chat_id

Instead of calling a /reset endpoint on platform-agent, !reset now
generates a new thread_id (platform_chat_id) for the room. The old
WebSocket connection is closed and the next message creates a fresh
context automatically. No platform changes required.

sdk/real.py

@@ -120,6 +120,15 @@ class RealPlatformClient(PlatformClient):
     async def update_settings(self, user_id: str, action) -> None:
         await self._prototype_state.update_settings(user_id, action)
 
+    async def disconnect_chat(self, chat_id: str) -> None:
+        chat_key = str(chat_id)
+        chat_api = self._chat_apis.pop(chat_key, None)
+        self._chat_send_locks.pop(chat_key, None)
+        if chat_api is not None:
+            close = getattr(chat_api, "close", None)
+            if callable(close):
+                await close()
+
     async def close(self) -> None:
         for chat_api in list(self._chat_apis.values()):
             close = getattr(chat_api, "close", None)