- Watched: an explicit toggle in the modal (Mark watched / Watched→unmark) plus
auto-mark when playback reaches the end (within 10s, or on the ended event).
- Compact layout: drop the header bar and the redundant 'Open on YouTube' button
(the embed's own YouTube logo already jumps out); Close moves to the title row,
channel + meta share one line — fits without a scrollbar at higher zoom.
- Card actions reflect status: watched shows a double-check, saved a filled
bookmark, with matching tooltips.
- Description: new GET /api/videos/{id} exposes the already-stored description,
shown in a popover when hovering the modal title (fetched lazily).
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