Track YouTube thumbnail 404 failures

[jsnmrs]

Summary

• Add persistent per-video tracking of thumbnail 404 failures via thumbnail_issue_count column on aggro_videos
• Pass HTTP status code through fetch_url() and fetch_thumbnail() so callers can distinguish 404s from other failures
• Flag videos as bad after exceeding 10 consecutive 404s, removing them from active queries and the sweep cycle
• Wire flagBrokenThumbnails() into the sweep after cleanThumbs()

Fixes AGGRO-1J

Post-deployment steps

After deploy, run the database migration on the production server:

php spark migrate

This adds the thumbnail_issue_count column to the end of aggro_videos. MySQL 8.0+ handles appended columns via instant DDL — no table copy, no locking.

Verify the column exists:

php spark db:table aggro_videos

No other manual steps are needed. Existing rows start at 0, and the counter begins incrementing on the next sweep cycle.

Test plan

• New ThumbnailService tests pass (increment, reset, flag broken, skip already-bad, return count)
• New AggroHelper tests pass (httpStatus populated, 404 detection, thumbnail passthrough, backward compatibility)
• Full test suite passes (464 tests, 0 failures)
• PHP CS Fixer clean
• PHPStan clean
• Run migration on production after deploy
• Verify AGGRO-1J stops recurring in Sentry after affected videos are flagged