Adds a paste-URL ingest path under Ingest → YouTube. Worker hosts
yt-dlp, downloads to S3, then hands off to the existing proxy +
thumbnail pipeline so imported assets share one lifecycle with uploads.
Co-Authored-By: Claude Opus 4.7 <noreply@anthropic.com>
Self-review caught an ordering ambiguity in the responsive section: 1280x800
is the fully-supported minimum, tablet 768-1279 is best-effort. Rewording
so the tiers list top-down by viewport size.
Full design spec for the flyon-ui-based shell rework. All 7 design
sections (build system, sidebar, topbar, cards, forms/slide-panel,
states/motion, a11y/responsive/rollout) approved by user during
brainstorming. Next step is the implementation plan via writing-plans.
