Implement and validate out-of-process Designer integration

[KlausLoeffelmann]

Objective

Coordinate the Designer-side recognition and generated-code behavior for the approved contract. Cover drag-and-drop, serialization, inherited designs, rename/remove operations, undo/redo, reload, and applications that do not use the builder.

Completion guidance

• Keep the implementation focused on the objective while allowing the assignee to improve the approach based on research.
• Document important decisions, rejected alternatives, dependencies, and follow-up work.
• Add or update tests and documentation appropriate to the work.
• Verify locally and in CI where the task changes code or generated artifacts.