refactor: update module docstrings for clarity and consistency

backend/app/services/admin_access.py

@@ -1,10 +1,16 @@
+"""Access control helpers for admin-only operations."""
+
 from __future__ import annotations
 
+from typing import TYPE_CHECKING
+
 from fastapi import HTTPException, status
 
-from app.core.auth import AuthContext
+if TYPE_CHECKING:
+    from app.core.auth import AuthContext
 
 
 def require_admin(auth: AuthContext) -> None:
+    """Raise HTTP 403 unless the authenticated actor is a user admin."""
     if auth.actor_type != "user" or auth.user is None:
         raise HTTPException(status_code=status.HTTP_403_FORBIDDEN)