a11y: exported semantics (forms/rating/nav/iframe/icons)

- InputField/TextareaField/ContactForm: every control gets a
  deterministic id (slugId() in utils/escape.ts, derived from the
  field's name/label + index for ContactForm's looped fields -- no
  Math.random) with a matching <label for=>; fields with no visible
  label get an aria-label from the placeholder/name instead.
- StarRating: wrapped in role="img" aria-label="Rating: N out of M",
  individual star glyphs marked aria-hidden.
- Navbar: the mobile hamburger toggle gets aria-label="Toggle
  navigation menu", aria-controls="navbar-links", and aria-expanded
  wired to flip true/false in the inline onclick handler.
- VideoBlock and MapEmbed: every exported <iframe> gets a title
  (generic "Embedded video", or "Map of {address}" for MapEmbed).
- Decorative Font Awesome icons (ContentSlider arrows already covered
  in the prior commit; SocialLinks, SearchBar, Testimonials stars) are
  aria-hidden; SocialLinks' icon-only links get an aria-label naming
  the platform alongside the existing title tooltip.

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

craft/src/components/media/VideoBlock.toHtml.test.ts

@@ -59,3 +59,15 @@ describe('VideoBlock URL parsing (D4)', () => {
     expect(html).not.toContain('javascript:');
   });
 });
+
+describe('VideoBlock.toHtml iframe accessibility (F2.4)', () => {
+  test('normal-mode YouTube/Vimeo iframe has a title attribute', () => {
+    const { html } = toHtml({ videoUrl: 'https://www.youtube.com/watch?v=dQw4w9WgXcQ' }, '');
+    expect(html).toMatch(/<iframe[^>]*title="[^"]+"/);
+  });
+
+  test('background-mode YouTube/Vimeo iframe has a title attribute', () => {
+    const { html } = toHtml({ videoUrl: 'https://vimeo.com/123456789', isBackground: true }, '');
+    expect(html).toMatch(/<iframe[^>]*title="[^"]+"/);
+  });
+});