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/modern-code-icon.svg

@@ -0,0 +1,10 @@
+<svg xmlns="http://www.w3.org/2000/svg" width="24" height="24" viewBox="0 0 24 24" 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>
+  <path d="M9 6L3 12L9 18" stroke="url(#gradient)" stroke-width="2.5" stroke-linecap="round" stroke-linejoin="round"/>
+  <path d="M15 6L21 12L15 18" stroke="url(#gradient)" stroke-width="2.5" stroke-linecap="round" stroke-linejoin="round"/>
+</svg>