Create a DI/scopes sample and exploratory compatibility matrix

## Objective

Build a sample with constructor-injected Forms, Designer-created UserControls/components, modal and modeless scopes, navigation, cancellation, and disposal diagnostics. Exercise C# and VB, Designer round trips, Classic/light/Dark Mode, Terminal Services, Windows on ARM, and slow hardware.

## 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.

No files, tests, or entry points are named. Start by researching the existing WinForms sample and DI/scopes infrastructure, then define the sample boundaries and compatibility matrix. Done means the requested C# and VB scenarios, Designer round trips, platform and theme checks, diagnostics, decisions, tests, and documentation are covered.

Written by the indexing model from the issue text.