Covers validators, response mapping, TagService/TagsController,
FeaturesController (CRUD + tag assignment), FeatureSegmentService,
FeatureStateService (incl. webhook dispatch), and
FeatureUsageController. Fills gaps in FeatureService
(FindByIdAsync, not-found exceptions).
FeatureUsageFlushBackgroundService is marked [ExcludeFromCodeCoverage]:
timer-driven, issues raw SQL through a DI-scoped concrete DbContext,
can't be exercised cleanly without a live DB (CLAUDE.md disallows
WebApplicationFactory/InMemory).
Raises the namespace from 44% to 97%.
## Summary
- Extract `IMicCheckDbContext` and mock DB access with Moq instead of the EF InMemory provider, per CLAUDE.md testing guidelines.
- Rewrite HTTP-pipeline tests to exercise controllers/auth handlers directly instead of `WebApplicationFactory`.
- Remove tuple return types across the API in favor of named records (`PagedResult<T>`, `ProfileUpdateResult`, `ApiKeyCreationResult`).
## Test plan
- [x] `dotnet build` (full solution)
- [x] `dotnet test tests/api/MicCheck.Api.Tests.Unit` — 187/187 pass
- [x] `dotnet test tests/api/MicCheck.Api.Tests.Integration` — 8/8 pass (live API + Postgres via Aspire)
- [x] Verified Aspire AppHost/dashboard starts and API responds
Reviewed-on: #4
