Health Check Status Transition

What Was Built

• Added trigger_fetch_if_degraded to SourceHealthCheckJob that enqueues FetchFeedJob.perform_later(source.id, force: true) after a successful health check on a degraded source (declining/critical/warning)
• Added 5 tests covering all degraded statuses, healthy source exclusion, and failed health check exclusion

Files Modified

• app/jobs/source_monitor/source_health_check_job.rb -- added DEGRADED_STATUSES constant, trigger_fetch_if_degraded private method, call in perform
• test/jobs/source_monitor/source_health_check_job_test.rb -- 5 new test cases (10 total, 46 assertions, 0 failures)