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>

tests/test_marketing_landing_template.py

@@ -112,10 +112,11 @@ def test_hero_has_cosmic_orbs_background():
 
 
 def test_hero_has_social_proof_microcopy():
-    """Hero has '27 cabinets' social proof + Lancement printemps 2026."""
+    """Hero has defensible social proof: 9 ordres pros + waitlist + launch date."""
     client = app.test_client()
     body = client.get('/').data.decode('utf-8')
-    assert '27 cabinets' in body, "Missing social proof '27 cabinets'"
+    assert '9 ordres professionnels' in body, "Missing factual ordres pros count"
+    assert 'Pré-inscription' in body or 'Pré-inscription' in body, "Missing waitlist mention"
     assert 'Lancement printemps 2026' in body, "Missing launch date"