Create automated lifetime and shutdown coverage and run it in CI

[KlausLoeffelmann]

Objective

Add focused unit and integration coverage for startup forms, custom application contexts, startup failures, cancellation, host-initiated shutdown, form-initiated shutdown, exception paths, and repeated runs where supported. Run locally and in the normal CI matrix; avoid timing-fragile tests.

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.