fix(radio): keyboard a11y — skip link, focus-visible, mobile-menu

human-flow P0-P1 fixes for radio.azcomputerguru.com:
- K1: skip-to-content link (first tab stop) + id/tabindex on <main>.
- K2: global :focus-visible ring (accent outline) across links, buttons,
  inputs and player controls; reveal the seek-bar handle on focus.
- K3: mobile menu a11y — aria-expanded/aria-controls, Escape closes and
  restores focus to the toggle, focus moves to first link on open.
All token-based, no emojis. Not built (node_modules absent on this host).

Co-Authored-By: Claude Opus 4.8 (1M context) <noreply@anthropic.com>

projects/radio-show/website/src/components/global/PersistentPlayer.tsx

@@ -644,6 +644,15 @@ export default function PersistentPlayer() {
           opacity: 1;
         }
 
+        .persistent-player__progress-bar:focus-visible {
+          outline: 2px solid var(--color-accent, hsl(200 85% 55%));
+          outline-offset: 2px;
+        }
+
+        .persistent-player__progress-bar:focus-visible .persistent-player__progress-handle {
+          opacity: 1;
+        }
+
         [data-theme="light"] .persistent-player__progress-bar {
           background: hsl(220 12% 85% / 0.5);
         }
@@ -755,6 +764,17 @@ export default function PersistentPlayer() {
           background: hsl(220 16% 92% / 0.6);
         }
 
+        .persistent-player__btn:focus-visible {
+          outline: 2px solid var(--color-accent, hsl(200 85% 55%));
+          outline-offset: 2px;
+          color: var(--color-text-primary, hsl(220 10% 92%));
+        }
+
+        .persistent-player__btn--play:focus-visible {
+          color: hsl(220 20% 8%);
+          box-shadow: 0 0 16px hsl(200 85% 55% / 0.3);
+        }
+
         .persistent-player__btn--play {
           width: 40px;
           height: 40px;