feat: add component reference wiring — get_referenceable, set_reference, batch_wire

Extends manage_components with 3 new actions for object reference fields:

- get_referenceable: list assignable scene objects and project assets for
  a component's reference field, with type filtering
- set_reference: assign an object reference via path, asset path, or
  instance ID, with SerializedProperty + Undo support
- batch_wire: wire multiple references atomically in one call, with
  validation-first approach and grouped Undo

C# uses SerializedObject/SerializedProperty for correct prefab override
tracking, dirty state, and Undo. Reference resolution supports scene
objects, project assets, and component auto-resolution from GameObjects.

Author: zaferdace