fix: review round 1 — row press after a rename, related reset, dead items on removal, honest Prev/Next

- A press that begins while a field in the row is edited only ends the editing (rowOpen latches it
  at pointerdown); the card layout's row press is now tested.
- A related video reset in the player forgets the session's stored position.
- Removing the playing video passes over known-dead items and steps the way it went.
- Prev/Next off only because of dead items stay focusable and say why (HU/EN).
- The docked bar's scroller leaves room for focus rings.
- A focus-opened About card is not closed by its own scroll into view.
- EN "Clear watch progress" for the video reset, distinct from a page's "Reset view".
- The signed-out title read goes to the page yt-dlp read; the retitle writes are conditional.
- Tests: the cap of three errors, the bar's own Fullscreen, the group glyph, the backfill's reads.

frontend/src/components/ui/unavailable.ts

@@ -0,0 +1,7 @@
+/** An unavailable control's props. With a reason it stays focusable (`aria-disabled`, which
+ *  `FocusSafeButton` keeps inert to a click, and the reason in its tooltip — DESIGN.md "Unavailable
+ *  with a reason stays focusable"); without one it is plainly off. */
+export function unavailable(disabled: boolean | undefined, reason: string | undefined) {
+  if (!disabled) return {};
+  return reason ? { "aria-disabled": true as const } : { disabled: true };
+}