fix(test-entity): resolve ValueError when coercing foreign TestState enum

str() on models.enums.TestState produces 'TestState.red_executing' instead of 'red_executing'. Use .value to extract the plain string before constructing the domain TestState.

backend/app/domain/test_entity.py

@@ -166,7 +166,8 @@ class TestEntity:
 
         Raises :class:`InvalidStateTransition` when the move is illegal.
         """
-        resolved = target if isinstance(target, TestState) else TestState(str(target))
+        value = target.value if hasattr(target, "value") else str(target)
+        resolved = target if isinstance(target, TestState) else TestState(value)
         return self._transition(resolved)
 
     def _transition(self, target: TestState) -> str: