fix(a11y): touch/keyboard reveal tail + single-Escape layer coordination (UX-7/UX-8)

UX-8: one Escape must close only the topmost layer, never both an open
popover AND the player beneath it. The popover's Escape listener is on
`document` and fires before the player's on `window`; closing the popover
flushes its layer off the shared stack synchronously, so the player's
`anyLayerAbove()` lookup read "nothing above" and closed too. Add a
consumed-event flag to layerStack (`markEscapeHandled`/`escapeHandled`):
the acting topmost layer stamps the shared KeyboardEvent, and both players
check the stamp before the (now-mutated) stack. Immune to listener order
and mid-dispatch stack mutation. Cover with layerStack.dom.test.ts.

UX-7: the E4 `.reveal` sweep already covered the card action rows; two
residual hover-only traps remained — invisible-but-tappable/Tab-focusable
on touch. Add a group-agnostic `.reveal-hover` recipe (display:none under
`(hover: none)`) paired with each site's own hover/focus-within reveal:
- VideoCard play/Continue/Restart overlay: also reveal on
  group-focus-within (keyboard), and drop it on touch — the card tap
  already plays/resumes, so no permanent scrim over every mobile thumbnail.
- Carousel prev/next arrows: gone on touch, where the strip swipes.

frontend/src/lib/layerStack.ts

@@ -38,6 +38,23 @@ export function anyLayerAbove(id: number): boolean {
   return i !== -1 && i < stack.length - 1;
 }
 
+// UX-8 — a layer that ACTS on an Escape stamps the event here; a lower layer with its own key handler
+// (the players, listening on `window`) reads the stamp instead of re-reading the stack. This closes
+// the "one Escape closes BOTH the popover and the player" bug: the popover's Escape listener is on
+// `document` and fires before the player's on `window` (bubble order), and closing the popover flushes
+// its layer off the stack synchronously — so by the time the player's `anyLayerAbove()` runs, the stack
+// already reads "nothing above" and the player ALSO closes. Tagging the one shared KeyboardEvent object
+// (every listener in a single dispatch is handed the same instance) is immune to that mid-dispatch
+// mutation; `anyLayerAbove` stays as the fallback for a layer above with no Escape handler of its own.
+// WeakSet so a spent event is GC'd without a manual sweep.
+const handledEscapes = new WeakSet<KeyboardEvent>();
+export function markEscapeHandled(e: KeyboardEvent): void {
+  handledEscapes.add(e);
+}
+export function escapeHandled(e: KeyboardEvent): boolean {
+  return handledEscapes.has(e);
+}
+
 /** Register an open layer for as long as `active` is true, and get live predicates to read inside your
  *  own key handler. Pass `onEscape` to also install a topmost-only Escape listener (the common case —
  *  modals, popovers). Omit it for a layer that owns a bigger key handler and only needs `anyAbove()`
@@ -57,7 +74,12 @@ export function useLayer(
     let onKey: ((e: KeyboardEvent) => void) | undefined;
     if (escRef.current) {
       onKey = (e: KeyboardEvent) => {
-        if (e.key === "Escape" && isTopmost(id)) escRef.current?.();
+        if (e.key === "Escape" && isTopmost(id)) {
+          // Stamp BEFORE closing so a player's `window` listener (fires after this `document` one)
+          // sees the Escape as consumed even though closing us pops this layer off the stack.
+          markEscapeHandled(e);
+          escRef.current?.();
+        }
       };
       document.addEventListener("keydown", onKey);
     }