feat(p0): complete account security privacy and sync hardening

app/chats/router.py

@@ -101,7 +101,10 @@ async def create_chat(
     current_user: User = Depends(get_current_user),
 ) -> ChatRead:
     chat = await create_chat_for_user(db, creator_id=current_user.id, payload=payload)
-    realtime_gateway.add_chat_subscription(chat_id=chat.id, user_id=current_user.id)
+    member_user_ids = await chats_repository.list_chat_member_user_ids(db, chat_id=chat.id)
+    for member_user_id in member_user_ids:
+        realtime_gateway.add_chat_subscription(chat_id=chat.id, user_id=member_user_id)
+    await realtime_gateway.publish_chat_updated(chat_id=chat.id)
     return await serialize_chat_for_user(db, user_id=current_user.id, chat=chat)
 
 
@@ -284,6 +287,7 @@ async def clear_chat(
     current_user: User = Depends(get_current_user),
 ) -> None:
     await clear_chat_for_user(db, chat_id=chat_id, user_id=current_user.id)
+    await realtime_gateway.publish_chat_updated(chat_id=chat_id)
 
 
 @router.post("/{chat_id}/pin", response_model=ChatRead)