feat(brand): logo officiel DictIA + palette blue/cyan/fuchsia (matche le logo)

Logos officiels installés :
- static/images/dictia-logo.png (28 KB optimisé 256×256)
- static/images/dictia-logo-128.png (10 KB retina)
- static/images/dictia-logo-fullres.png (originaux conservés OG/social)
- static/images/dictia-logo.svg + dictia-logo-nom.svg (cleaned C2PA metadata)
- Header marketing/base.html : <img> 40×40 + wordmark "DictIA" + tagline "Transcription"
- Footer marketing/_footer.html : <img> 36×36 + wordmark
- Favicon mis à jour vers logo PNG

Note : SVG sources sont des PNG base64 wrappés (pas de vrais paths) — PNG utilisé
en production (8× plus léger), SVG conservé pour fallback.

Palette canonique alignée sur le logo :
- brand-b1 : #7c3aed (mauve) → #2563eb (blue-600 vibrant — primary)
- brand-b2 : #a855f7 (mauve clair) → #06b6d4 (cyan-500 — aqua mid)
- brand-b3 : #06b6d4 (aqua) → #c026d3 (fuchsia-600 — magenta accent)
- Gradient signature : linear-gradient(118deg, #2563eb, #06b6d4 52%, #c026d3)
- Box shadow CTA : rgba(37,99,235,0.28/0.42)
- 72 remplacements hex/rgba dans 5 templates marketing/legal + email service

Tests : 81 passed / 3 failed (3 échecs pré-existants /blog + trust-bar phrasing,
non liés à ce changement). 0 régression.

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

static/css/tailwind.config.js

@@ -6,9 +6,9 @@ module.exports = {
     extend: {
       colors: {
         brand: {
-          b1: '#7c3aed',
-          b2: '#a855f7',
-          b3: '#06b6d4',
+          b1: '#2563eb',
+          b2: '#06b6d4',
+          b3: '#c026d3',
           navy: '#060d1a',
           navy2: '#0b1525',
           navy3: '#0f1e35',
@@ -21,11 +21,11 @@ module.exports = {
         mono: ['JetBrains Mono Variable', 'JetBrains Mono', 'monospace'],
       },
       backgroundImage: {
-        'brand-grad': 'linear-gradient(118deg, #7c3aed, #a855f7 52%, #06b6d4)',
+        'brand-grad': 'linear-gradient(118deg, #2563eb, #06b6d4 52%, #c026d3)',
       },
       boxShadow: {
-        'cta': '0 4px 20px rgba(124, 58, 237, 0.28)',
-        'cta-hover': '0 8px 32px rgba(124, 58, 237, 0.42)',
+        'cta': '0 4px 20px rgba(37, 99, 235, 0.28)',
+        'cta-hover': '0 8px 32px rgba(37, 99, 235, 0.42)',
       },
       borderRadius: {
         DEFAULT: '0.75rem',
@@ -44,8 +44,8 @@ module.exports = {
           '50%': { transform: 'translateY(-8px)' },
         },
         'tc-pulse-glow': {
-          '0%, 100%': { boxShadow: '0 4px 20px rgba(124, 58, 237, 0.28)' },
-          '50%': { boxShadow: '0 8px 32px rgba(124, 58, 237, 0.42)' },
+          '0%, 100%': { boxShadow: '0 4px 20px rgba(37, 99, 235, 0.28)' },
+          '50%': { boxShadow: '0 8px 32px rgba(37, 99, 235, 0.42)' },
         },
         'plus-breathe': {
           '0%, 100%': { transform: 'scale(1)' },