Create migration, enterprise, system-tray, and backend samples

## Objective

Provide focused samples or solution templates only where they teach materially different architecture: incremental migration, layered enterprise composition, application-context/system-tray lifetime, and optional backend/cloud integration. Keep samples illustrative rather than prescriptive frameworks.

## 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 surveying the repository’s existing samples and solution templates to identify where these examples belong and how they should be structured. Define focused examples for incremental migration, layered enterprise composition, system-tray lifetime, and optional backend/cloud integration, then document decisions, rejected alternatives, dependencies, and follow-up work. Add appropriate tests and documentation, and verify locally and in CI.

Written by the indexing model from the issue text.