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.tsx

@@ -403,7 +403,7 @@ VideoBlock.craft = {
         zIndex: '0',
         pointerEvents: 'none',
       });
-      videoHtml = `<iframe src="${escapeAttr(safeUrl(iframeSrc))}" allow="autoplay; encrypted-media" allowfullscreen${ifrStyle ? ` style="${ifrStyle}"` : ''}></iframe>`;
+      videoHtml = `<iframe src="${escapeAttr(safeUrl(iframeSrc))}" title="Embedded video" allow="autoplay; encrypted-media" allowfullscreen${ifrStyle ? ` style="${ifrStyle}"` : ''}></iframe>`;
     }
 
     return {
@@ -436,7 +436,7 @@ VideoBlock.craft = {
       border: 'none',
     });
     return {
-      html: `<div${wrapperStyle ? ` style="${wrapperStyle}"` : ''}><div${containerStyle ? ` style="${containerStyle}"` : ''}><iframe src="${escapeAttr(safeUrl(iframeSrc))}" allow="autoplay; encrypted-media; picture-in-picture" allowfullscreen${iframeStyle ? ` style="${iframeStyle}"` : ''}></iframe></div></div>`,
+      html: `<div${wrapperStyle ? ` style="${wrapperStyle}"` : ''}><div${containerStyle ? ` style="${containerStyle}"` : ''}><iframe src="${escapeAttr(safeUrl(iframeSrc))}" title="Embedded video" allow="autoplay; encrypted-media; picture-in-picture" allowfullscreen${iframeStyle ? ` style="${iframeStyle}"` : ''}></iframe></div></div>`,
     };
   }