refactor: standardize test mocks to use shared mock files

[kevinrutledge]

Developer

Kevin Rutledge

What changed?

Standardized test mock patterns across the codebase. Three files were using inline mocks where shared mock files already exist.

1. contact-group.test.ts - replaced inline vi.mock() for next/cache and @/lib/dal with shared mock imports (import "../mocks/next-cache" and import "../mocks/dal"). Service mocks stay inline since they're only used in this one file. This was the oldest action test file (Feb 14) and was never updated when the shared mock pattern was adopted.

2. encryption.ts mock - added beforeEach with vi.clearAllMocks() to clear call history between tests. Uses clearAllMocks (not resetAllMocks) because the passthrough implementations (encrypt returns input, blindIndex hashes) need to persist. Every other shared mock file with vi.fn() calls already had a reset hook.

3. auth-flow.test.ts - removed stale TODO comment that duplicated a source-level TODO in src/actions/auth.ts. Test comments should not carry forward source-level implementation notes.

How to test

1. Run npm test - 272 tests pass
2. Run npm run build - succeeds

Checklist

• Code works and is readable
• Tested locally
• Commits follow conventional commits
• Assigned reviewers