fix(marketing): WCAG 2.3.3 reduced-motion + defensible social proof + em-spacing

- Add @media (prefers-reduced-motion: reduce) override to disable animations
  for vestibular-sensitive users (covers hero + future scroll/infinite anims)
- Replace 5-star icon + '27 cabinets' claim with shield + 'Conçu avec 9
  ordres professionnels' + 'Pré-inscription ouverte' (LPC art. 219 +
  Competition Act s. 52 compliance — pre-launch claims must be factual)
- Convert H1/H2/H3 letter-spacing from absolute px to em-relative (-3px →
  -0.028em on H1) so tracking scales correctly with clamp font-size on mobile
- Update test_hero_has_social_proof_microcopy to assert new copy

Co-Authored-By: Claude Opus 4.7 (1M context) <noreply@anthropic.com>

static/css/input.css

@@ -17,8 +17,8 @@
   body {
     @apply font-sans bg-white text-brand-navy antialiased;
   }
-  h1, h2, h3 { @apply font-black; letter-spacing: -2.5px; }
-  h1 { letter-spacing: -3px; }
+  h1, h2, h3 { @apply font-black; letter-spacing: -0.022em; }
+  h1 { letter-spacing: -0.028em; }
 }
 
 @layer utilities {
@@ -32,3 +32,15 @@
     @apply text-[11px] uppercase font-bold tracking-[0.18em];
   }
 }
+
+/* WCAG 2.3.3 — respect user's motion preference */
+@media (prefers-reduced-motion: reduce) {
+  *,
+  *::before,
+  *::after {
+    animation-duration: 0.01ms !important;
+    animation-iteration-count: 1 !important;
+    transition-duration: 0.01ms !important;
+    scroll-behavior: auto !important;
+  }
+}