feat(ui): modernize design with gradient icons and animations

- Add modern-code-icon.svg and update favicon with gradient styling
- Implement glass effect, hover animations and gradient text in global.css
- Enhance GlassHeader with motion animations and new icon
- Update design variables for modern look including shadows and transitions

public/favicon.svg

@@ -1,9 +1,16 @@
-<svg xmlns="http://www.w3.org/2000/svg" fill="none" viewBox="0 0 128 128">
-    <path d="M50.4 78.5a75.1 75.1 0 0 0-28.5 6.9l24.2-65.7c.7-2 1.9-3.2 3.4-3.2h29c1.5 0 2.7 1.2 3.4 3.2l24.2 65.7s-11.6-7-28.5-7L67 45.5c-.4-1.7-1.6-2.8-2.9-2.8-1.3 0-2.5 1.1-2.9 2.7L50.4 78.5Zm-1.1 28.2Zm-4.2-20.2c-2 6.6-.6 15.8 4.2 20.2a17.5 17.5 0 0 1 .2-.7 5.5 5.5 0 0 1 5.7-4.5c2.8.1 4.3 1.5 4.7 4.7.2 1.1.2 2.3.2 3.5v.4c0 2.7.7 5.2 2.2 7.4a13 13 0 0 0 5.7 4.9v-.3l-.2-.3c-1.8-5.6-.5-9.5 4.4-12.8l1.5-1a73 73 0 0 0 3.2-2.2 16 16 0 0 0 6.8-11.4c.3-2 .1-4-.6-6l-.8.6-1.6 1a37 37 0 0 1-22.4 2.7c-5-.7-9.7-2-13.2-6.2Z" />
-    <style>
-        path { fill: #000; }
-        @media (prefers-color-scheme: dark) {
-            path { fill: #FFF; }
-        }
-    </style>
+<svg xmlns="http://www.w3.org/2000/svg" width="128" height="128" viewBox="0 0 128 128" fill="none">
+  <defs>
+    <linearGradient id="gradient" x1="0%" y1="0%" x2="100%" y2="100%">
+      <stop offset="0%" stop-color="#8B5CF6" />
+      <stop offset="100%" stop-color="#EC4899" />
+    </linearGradient>
+  </defs>
+  <rect width="128" height="128" rx="24" fill="white" class="dark:fill-black" />
+  <path d="M42 38L24 64L42 90" stroke="url(#gradient)" stroke-width="10" stroke-linecap="round" stroke-linejoin="round"/>
+  <path d="M86 38L104 64L86 90" stroke="url(#gradient)" stroke-width="10" stroke-linecap="round" stroke-linejoin="round"/>
+  <style>
+    @media (prefers-color-scheme: dark) {
+      .dark\:fill-black { fill: #000; }
+    }
+  </style>
 </svg>