security: rename misleading require_admin to require_user_actor

The function only checked that the caller was an authenticated user
(not an agent) but its name implied privilege enforcement. Rename to
require_user_actor and add docstring clarifying the distinction between
actor-type checks and privilege/role checks (require_org_admin, is_super_admin).

Co-Authored-By: Claude Opus 4.6 <noreply@anthropic.com>

backend/app/services/admin_access.py

@@ -1,4 +1,4 @@
-"""Access control helpers for admin-only operations."""
+"""Access control helpers for actor-type checks."""
 
 from __future__ import annotations
 
@@ -10,7 +10,12 @@ 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."""
+def require_user_actor(auth: AuthContext) -> None:
+    """Raise HTTP 403 unless the authenticated actor is a human user (not an agent).
+
+    NOTE: This is an actor-type check, NOT a privilege/role check.
+    For admin privilege enforcement, use ``require_org_admin`` (organization-level)
+    or check ``user.is_super_admin`` (global-level).
+    """
     if auth.actor_type != "user" or auth.user is None:
         raise HTTPException(status_code=status.HTTP_403_FORBIDDEN)