Adds OAuth 2.0 flow to connect a YouTube account and sync liked
videos as "like" posts on the blog. Includes:
- OAuth authorize/callback/disconnect flow with token persistence
- getLikedVideos() method using videos.list?myRating=like
- Background periodic sync + manual sync trigger
- Dashboard UI for connection status and sync controls
- Public JSON API for querying synced likes
Co-Authored-By: Claude Opus 4.6 <noreply@anthropic.com>
