feat(search): add unified global search for users/chats/messages

app/search/schemas.py

@@ -0,0 +1,12 @@
+from pydantic import BaseModel
+
+from app.chats.schemas import ChatDiscoverRead
+from app.messages.schemas import MessageRead
+from app.users.schemas import UserSearchRead
+
+
+class GlobalSearchRead(BaseModel):
+    users: list[UserSearchRead]
+    chats: list[ChatDiscoverRead]
+    messages: list[MessageRead]
+