feat(design): a video's one action list (C1) — the card's "…", the menu holds the rest (E28 S3e1)

- useContextMenu gains buttonProps (a row's visible "…" opens the same menu under the button; a
  second press closes it) and anchor (the element the menu came from, for a panel a row opens).
- ui/MoreButton; ActionMenu rows can run inGesture (a clipboard write inside the click, Safari).
- useVideoActions: one builder for a video's menu (play / restart, channel, watched, save, add to
  playlist, download, details, copy title / link, hide, reset, pin), composed by the feed and by
  Home's rails; the playlists and details panels open anchored beside the card (VideoFollowUp).
- The card keeps watched / save / add to playlist and the "…": on the picture on hover (the
  duration steps aside), in the rows' action column; on touch only a 44px "…" beside the title.
  Download, hide, reset and the hover info card leave the card.
- The title is selectable: a click ending a selection neither plays nor follows the link.
- DESIGN.md: how C1 is built + the log row.

frontend/src/index.css

@@ -737,6 +737,12 @@ body {
   .group:focus-within .reveal-idle {
     opacity: 0;
   }
+  /* The mirror of `.reveal-hover`: a control that exists ONLY on touch, because a mouse reaches the
+     same action another way — the video card's "…" beside the title, whose mouse twin sits in the
+     hover row on the picture (E28 C1). `display: none`, so it is no Tab stop either. */
+  .touch-only {
+    display: none;
+  }
 }
 @media (hover: none) {
   .reveal-idle {