Implement scope-aware Form, UserControl, and component activation

[KlausLoeffelmann]

Objective

Implement approved activation and scope behavior for common UI lifetimes, including modal and modeless Forms, nested UserControls, components, factories/navigation, disposal ordering, and failure cleanup. Do not introduce a process-wide static service locator.

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.