- YouTube sort=p fetch: indexes top 100 most-viewed videos from a channel,
storing view_count in the DB
- Popular tab on channel page shows videos sorted by view_count DESC
- Videos/Popular tab switcher with context-appropriate fetch buttons
- Expose view_count in VideoOut; add 'popular' sort to channel videos endpoint
Co-Authored-By: Claude Sonnet 4.6 <noreply@anthropic.com>