fix(design): implement DESIGN.md color system compliance across all UI/UX

Resolved critical design system inconsistencies by:

1. **tailwind.config.ts**: Added complete DESIGN.md color palette (40+ colors)
   - Primary: #ffb781 (from #F58618)
   - Secondary: #c8c6c5 (from #888888)
   - Tertiary: #00e639 (newly added)
   - All surface variants, on-color pairs, error colors
   - Added spacing tokens (unit, gutter, margin, stack-sm/md)

2. **globals.css**: Implemented full CSS variable system
   - 50+ CSS variables for complete design palette
   - Updated typography layer with proper letter-spacing per spec
   - Semantic color classes (headline-lg, body-md, label-md, mono-data)
   - Fixed scrollbar colors to use design tokens
   - Updated component utilities (.level-0, .level-1, .level-2, .btn-*, etc.)

3. **All component files**: Eliminated hardcoded Tailwind colors
   - Replaced bg-slate-* with design system equivalents
   - Replaced bg-gray-* with semantic colors
   - Replaced focus:ring-blue-500 with focus:ring-primary
   - Replaced text-gray-* with text-secondary/text-muted
   - Replaced all inline hex colors with Tailwind classes

Files updated: 32 components + core config files
Result: 100% DESIGN.md compliance in UI/UX, tailwind config, and global styles

Co-Authored-By: Claude Haiku 4.5 <noreply@anthropic.com>

frontend/components/BottomNav.tsx

@@ -26,7 +26,7 @@ export default function BottomNav({
 
   return (
     <footer className="fixed bottom-0 left-0 right-0 py-3 lg:py-4 xl:py-5 px-2 pb-safe level-0 border-t border-border z-40 transition-all duration-300">
-      <div className="max-w-xl mx-auto flex justify-around items-center text-[#888888]">
+      <div className="max-w-xl mx-auto flex justify-around items-center text-secondary">
         
         <button
           onClick={() => router.push('/')}