Create VB-to-shared-model and C# feature samples with migration guidance

## Objective

Create paired VB and C# samples plus an incremental migration example from `ApplicationEvents.vb`/MyApplication to the shared model. Show how existing VB projects remain valid, how applications opt in feature-by-feature, and where behavior intentionally differs.

## 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.

Start by locating the existing ApplicationEvents.vb/MyApplication material and the shared-model entry points, then compare the VB and C# sample patterns. Done means paired samples and an incremental migration example explain compatibility, feature opt-in, intentional differences, decisions, dependencies, and follow-up work, with appropriate tests and documentation verified locally and in CI.

Written by the indexing model from the issue text.