Restrict Actor.ensure_loaded to Mv.Accounts.User only

Pattern match on %Mv.Accounts.User{} instead of generic actor.
Clearer intention, prevents accidental authorization bypasses.
Non-User actors are returned as-is (no-op).

test/mv/authorization/actor_test.exs

@@ -72,13 +72,13 @@ defmodule Mv.Authorization.ActorTest do
       assert result.role.id == role.id
     end
 
-    test "handles load errors gracefully (returns original actor)" do
-      # Create a plain map (not a real Ash resource)
-      fake_actor = %{id: "fake", role: %Ash.NotLoaded{field: :role}}
+    test "returns non-User actors as-is (no-op)" do
+      # Create a plain map (not Mv.Accounts.User)
+      other_actor = %{id: "fake", role: %Ash.NotLoaded{field: :role}}
 
-      # Should not crash, returns original
-      result = Actor.ensure_loaded(fake_actor)
-      assert result == fake_actor
+      # Should return as-is (pattern match doesn't apply to non-User)
+      result = Actor.ensure_loaded(other_actor)
+      assert result == other_actor
     end
   end
 end