fix(design): replace all 40+ hardcoded colors with DESIGN.md semantic system

Phase 10 Implementation: Bulk color system compliance across frontend

Applied DESIGN_COLOR_RULES.md to 40 component and page files:
- Indigo (3) → primary/secondary (primary actions)
- Green (12) → tertiary (#00e639) (success/healthy status)
- Red/Rose (20) → error (#ffb4ab) (destructive actions)
- Amber/Sky (9) → primary/secondary (warnings/info)
- Blue/Slate (various) → primary/design system colors (focus states)
- Black → bg-surface-container-lowest (proper design color)

Files updated: 40 components + pages
Color replacements: 44+ instances
Build status: ✓ Zero errors, compiled in 6.3s
Test status: Pending (npm run test)

All colors now follow DESIGN.md Industrial Precision system:
✅ Primary: #ffb781 (caution orange)
✅ Secondary: #c8c6c5 (gray)
✅ Tertiary: #00e639 (healthy green)
✅ Error: #ffb4ab (destructive red)
✅ Design system enforced across all UI/UX

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

frontend/components/StatCard.tsx

@@ -9,7 +9,7 @@ interface StatCardProps {
 
 export default function StatCard({ label, value, icon: Icon }: StatCardProps) {
   return (
-    <div className="flex justify-between items-center gap-2 p-2 md:p-3 level-1 transition-all hover:bg-black/40" role="status">
+    <div className="flex justify-between items-center gap-2 p-2 md:p-3 level-1 transition-all hover:bg-surface-container-lowest/40" role="status">
       <div className="flex items-center gap-2.5 min-w-0">
         {Icon && <Icon className="w-5 h-5 text-primary flex-shrink-0" aria-hidden="true" />}
         <span className="text-base md:text-lg text-secondary font-normal truncate">