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/utils/escape.ts

@@ -78,3 +78,14 @@ export function safeUrl(s: string): string {
 
   return trimmed;
 }
+
+/**
+ * Derives a deterministic, HTML-id-safe slug from a field's `name`/`label`
+ * for wiring `<label for>` to a matching `<input id>` in exported markup.
+ * Pure function of the input string -- no Math.random/Date.now -- so the
+ * same field always gets the same id across export runs.
+ */
+export function slugId(s: string | undefined, fallback = 'field'): string {
+  const base = (s || '').toString().toLowerCase().replace(/[^a-z0-9]+/g, '-').replace(/^-+|-+$/g, '');
+  return base || fallback;
+}