Bug: community_scheduler always had status='ready' even when individual
sources were failed or stale. Success of one source masked failure of another.
Fix:
- Overall status is 'degraded' if any enabled source has failed
- Overall status is 'stale' if all sources are stale but none failed
- Overall status is 'ready' only when at least one source is healthy
- Overall status is 'not_started' when no sources are enabled
- Readiness (ready flag) still NOT blocked by import health (A01 requirement)
Verification:
- 7/7 readiness tests pass
- 121/121 Python tests pass (1 skipped)
- Failed/stale sources are now visible in JSON without blocking scheduler
- Infrastructure (DB/MinIO) blocks readiness; imports are diagnostic only
- Per-source community scheduler health with backoff detection
- Stale/failed imports never block /ready — scheduler can recover them
- Add 'blocking: false' to all import components
- 4 new tests: per-source health, backoff detection, stale/failed non-blocking
- 108 Python tests pass
- Add 'ready = ready and healthy' for community_scheduler check
- Add 'ready = False' for community_scheduler exception path
- Add 3 unit tests: success=ready, stale=not_ready, failed=not_ready
- Monitoring now correctly reports community import health
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