refactor: standardize runtime annotation types across multiple files

backend/app/schemas/activity_events.py

@@ -2,11 +2,13 @@
 
 from __future__ import annotations
 
-from datetime import datetime  # noqa: TCH003
-from uuid import UUID  # noqa: TCH003
+from datetime import datetime
+from uuid import UUID
 
 from sqlmodel import SQLModel
 
+RUNTIME_ANNOTATION_TYPES = (datetime, UUID)
+
 
 class ActivityEventRead(SQLModel):
     """Serialized activity event payload returned by activity endpoints."""