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/lib/textSelection.ts

@@ -0,0 +1,15 @@
+// docs/DESIGN.md "Text stays selectable": a click that ends a text selection does nothing. The
+// mouseup of a drag-select fires a click on whatever the drag started in, so a title that opens its
+// video on click would play it the moment the reader finished selecting its words to copy them.
+// A plain click collapses any selection on mousedown, so a non-empty selection that touches the
+// element at click time can only be the one this gesture just made.
+
+/** True when the page's selection is non-empty and starts or ends inside `el`. */
+export function endsTextSelection(el: Element): boolean {
+  const sel = typeof window === "undefined" ? null : window.getSelection();
+  if (!sel || sel.isCollapsed || !sel.toString().trim()) return false;
+  return (
+    (!!sel.anchorNode && el.contains(sel.anchorNode)) ||
+    (!!sel.focusNode && el.contains(sel.focusNode))
+  );
+}