PM-6012 support active challenges in any current phase

[jmgasper]

Summary

• add a hasCurrentPhase challenge-search filter backed by current phase names and open phase records
• document the distinction between public Active listings, registration-only listings, and member resource searches
• add database-backed regression coverage for scheduled versus current-phase challenges

Validation

• pnpm lint
• pnpm build
• targeted ChallengeService regression test (1 passing)

The full unit command was also exercised locally; unrelated existing tests require additional mock/integration configuration and fail outside the configured service environment.