realtime: emit and handle chat_deleted for full chat removals

docs/realtime.md

@@ -211,7 +211,21 @@ Sent when chat metadata/membership/roles/title changes:
 }
 ```
 
-## 3.8 `error`
+## 3.8 `chat_deleted`
+
+Sent when a chat is removed for all members/subscribers:
+
+```json
+{
+  "event": "chat_deleted",
+  "payload": {
+    "chat_id": 10
+  },
+  "timestamp": "2026-03-08T12:00:00Z"
+}
+```
+
+## 3.9 `error`
 
 Validation/runtime error during WS processing:
 
@@ -236,6 +250,7 @@ Validation/runtime error during WS processing:
 - Send periodic `ping` and expect `pong`.
 - Reconnect with exponential backoff.
 - On `chat_updated`, refresh chat metadata via REST (`GET /api/v1/chats` or `GET /api/v1/chats/{chat_id}`).
+- On `chat_deleted`, remove the chat from local state immediately and clear active-chat selection if needed.
 - On reconnect/visibility restore, reconcile state by reloading already-opened chats/messages via REST
   to recover missed `message_deleted`/delivery updates after transient disconnects or backend restarts.
 - For browser notifications, mentions (`@username`) should be treated as high-priority and can bypass