Two validation refinements so 'nothing new but junk candidates' stops
alarming as FAILED (reuters-markets case: 18 candidates, 16 deduped, the
only 2 new ones rejected as non-article pages):
- majority-failure rule downgrades to a warning when source_exhausted and
  every failure is a non-article rejection (og:type/body), same standing
  as all_seen
- preloaded per-URL INVALID_OUTPUT failures no longer set task-failed
  (task-level no-URL failures and RUNTIME/PERMISSION still fatal); the
  per-article signal already lives in counts and warnings