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/app/items/create.tsx

@@ -119,8 +119,8 @@ export default function CreateItemPage() {
             isActive
               ? 'bg-primary text-white'
               : isCompleted
-                ? 'bg-slate-400 text-white'
-                : 'bg-[#222222]'
+                ? 'bg-secondary text-white'
+                : 'bg-border'
           }`}
         >
           {stepNum}
@@ -320,7 +320,7 @@ export default function CreateItemPage() {
               <button
                 onClick={nextStep}
                 disabled={!uploadedPhoto}
-                className="flex-1 px-4 py-2 bg-primary text-white rounded-none hover:bg-primary/90 disabled:bg-[#222222] disabled:text-secondary transition-colors font-normal flex items-center justify-center gap-2"
+                className="flex-1 px-4 py-2 bg-primary text-white rounded-none hover:bg-primary/90 disabled:bg-border disabled:text-secondary transition-colors font-normal flex items-center justify-center gap-2"
               >
                 <ChevronRight size={16} />
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