realtime: emit and handle chat_deleted for full chat removals

app/realtime/schemas.py

@@ -20,6 +20,7 @@ RealtimeEventName = Literal[
     "user_online",
     "user_offline",
     "chat_updated",
+    "chat_deleted",
     "pong",
     "error",
 ]

app/realtime/service.py

@@ -162,6 +162,13 @@ class RealtimeGateway:
             payload={"chat_id": chat_id},
         )
 
+    async def publish_chat_deleted(self, *, chat_id: int) -> None:
+        await self._publish_chat_event(
+            chat_id,
+            event="chat_deleted",
+            payload={"chat_id": chat_id},
+        )
+
     async def disconnect_user(self, user_id: int, *, code: int = 4401, reason: str = "Session revoked") -> None:
         user_connections = self._connections.get(user_id, {})
         if not user_connections: