test: add missing test suites for frontend hooks and backend services

[therealjhay]

1. Frontend: Watchlist Hook Tests
   File:
   useWatchlist.test.tsx

Mocked the MSW server environment as per frontend testing standards, although the hook relies on localStorage interactions without external API calls.
Covered all major hook functionality including initializing the default state, adding/removing assets, reordering logic, handling watchlists creation, and full import/export flows while validating state persistence.
2. Backend: Usage Metrics Service Tests
File:
usageMetrics.service.test.ts

Utilized vi.mock for the Knex database and application loggers inline with your backend factory strategies.
Covered the UsageMetricsService.record fire-and-forget methods natively, including error handling.
Validated queryAggregates behavior when using both custom buckets/date ranges and default fallback values.
3. Backend: Source Normalization Service Tests
File:
sourceNormalization.service.test.ts

Instantiated a custom TestAdapter that implements ProviderAdapter and registered it with adapterRegistry to simulate full lifecycle mapping, validation, and normalization.
Handled the validation rejection paths and error generation for missing/conflicting adapter schemas.
Validated correct structural data transformations (merging unmapped fields to raw) when saving normalized outputs to the database helper.
4. Backend: Audit Retention Job Tests
File:
auditRetention.job.test.ts

Mimicked the mocking strategy found in supplyVerification jobs.
Fully mocked the injected auditService.applyRetentionPolicy and tested happy paths, overriding the default retention limit, edge cases of returning zero deletions, and error boundaries resulting from failed job executions.

Closes #759
Closes #755
Closes #752
Closes #767

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