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>

templates/marketing/fonctionnalites.html

@@ -15,7 +15,7 @@
     bottom: -10px;
     width: 0;
     height: 3px;
-    background: linear-gradient(118deg, #7c3aed, #a855f7 52%, #06b6d4);
+    background: linear-gradient(118deg, #2563eb, #06b6d4 52%, #06b6d4);
     transform: translateX(-50%);
     transition: width 600ms ease-out;
   }
@@ -27,16 +27,16 @@
 
   /* Hover lift cards */
   .ani-lift { transition: transform 200ms ease-out, box-shadow 200ms ease-out; }
-  .ani-lift:hover { transform: translateY(-2px); box-shadow: 0 8px 32px rgba(124, 58, 237, 0.18); }
+  .ani-lift:hover { transform: translateY(-2px); box-shadow: 0 8px 32px rgba(37,99,235, 0.18); }
 
   /* Sticky sub-nav active link */
-  .subnav-link[aria-current="true"] { color: #7c3aed; }
+  .subnav-link[aria-current="true"] { color: #2563eb; }
   .subnav-link[aria-current="true"]::after {
     content: '';
     display: block;
     height: 2px;
     margin-top: 4px;
-    background: linear-gradient(118deg, #7c3aed, #a855f7 52%, #06b6d4);
+    background: linear-gradient(118deg, #2563eb, #06b6d4 52%, #06b6d4);
   }
 
   /* Cosmic float orbs (n'utilise pas tc-float-y pour éviter rebuild) */
@@ -46,8 +46,8 @@
 
   /* DictIA Cloud pulse glow */
   @keyframes card-pulse-glow {
-    0%, 100% { box-shadow: 0 4px 20px rgba(124, 58, 237, 0.28); }
-    50% { box-shadow: 0 12px 40px rgba(124, 58, 237, 0.5); }
+    0%, 100% { box-shadow: 0 4px 20px rgba(37,99,235, 0.28); }
+    50% { box-shadow: 0 12px 40px rgba(37,99,235, 0.5); }
   }
   .card-pulse-glow { animation: card-pulse-glow 3s ease-in-out infinite; }
 
@@ -76,13 +76,13 @@
   {# Cosmic orbs background — float animation subtile #}
   <div class="absolute inset-0 pointer-events-none" aria-hidden="true">
     <div class="orb-float-a absolute top-1/4 left-1/4 w-[600px] h-[600px] rounded-full"
-         style="background: radial-gradient(circle, rgba(124,58,237,0.16) 0%, transparent 60%); filter: blur(40px);"></div>
+         style="background: radial-gradient(circle, rgba(37,99,235,0.16) 0%, transparent 60%); filter: blur(40px);"></div>
     <div class="orb-float-b absolute top-1/2 right-1/4 w-[500px] h-[500px] rounded-full"
          style="background: radial-gradient(circle, rgba(6,182,212,0.07) 0%, transparent 60%); filter: blur(40px);"></div>
     <div class="absolute inset-0"
          style="background-image: linear-gradient(rgba(255,255,255,0.02) 1px, transparent 1px), linear-gradient(90deg, rgba(255,255,255,0.02) 1px, transparent 1px); background-size: 40px 40px;"></div>
     <div class="absolute top-1/3 left-0 right-0 h-px"
-         style="background: linear-gradient(90deg, transparent, rgba(124,58,237,0.3), rgba(6,182,212,0.2), transparent);"></div>
+         style="background: linear-gradient(90deg, transparent, rgba(37,99,235,0.3), rgba(6,182,212,0.2), transparent);"></div>
   </div>
 
   <div class="relative max-w-[1200px] mx-auto px-6 text-center">