Define configuration, settings, logging, and desktop-service boundaries

## Objective

Map the Epic proposal onto existing `Microsoft.Extensions.*` contracts. Decide what WinForms must own versus reuse, define configuration precedence and environment behavior, and specify user-settings persistence/migration, exception routing, background-service, and health-diagnostic boundaries.

## 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 reviewing the Epic proposal and the existing Microsoft.Extensions.* contracts to map configuration, settings, logging, desktop-service, exception, background-service, and health-diagnostic responsibilities. Document the chosen boundaries, configuration and environment behavior, persistence and migration decisions, rejected alternatives, dependencies, and follow-up work, then add appropriate tests and documentation and verify locally and in CI.

Written by the indexing model from the issue text.