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/styles/global.css

@@ -31,6 +31,40 @@ a:hover {
   color: var(--color-accent-hover);
 }
 
+/* Global keyboard focus styles — strong, consistent ring on the dark theme.
+   Uses outline so it layers over any existing box-shadow focus rings. */
+a:focus-visible,
+button:focus-visible,
+[tabindex]:focus-visible,
+input:focus-visible,
+select:focus-visible,
+textarea:focus-visible {
+  outline: 2px solid var(--color-accent);
+  outline-offset: 2px;
+  border-radius: var(--radius-sm);
+}
+
+/* Skip to content link — keyboard-reachable first tab stop, hidden until focused */
+.skip-link {
+  position: absolute;
+  left: -9999px;
+  top: 0;
+  z-index: 1001;
+  padding: var(--space-3) var(--space-6);
+  background: var(--color-bg-secondary);
+  color: var(--color-accent);
+  border: 1px solid var(--color-border);
+  border-radius: var(--radius-sm);
+  font-size: var(--text-sm);
+  font-weight: 600;
+}
+.skip-link:focus {
+  left: var(--space-4);
+  top: var(--space-4);
+  outline: 2px solid var(--color-accent);
+  outline-offset: 2px;
+}
+
 img, video {
   max-width: 100%;
   height: auto;