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/inventory/QuantityDisplay.tsx

@@ -83,12 +83,12 @@ export default function QuantityDisplay({
 
   if (isEditing) {
     return (
-      <div className="flex items-center gap-2 bg-black border border-border px-3 py-2">
+      <div className="flex items-center gap-2 bg-surface-container-lowest border border-border px-3 py-2">
         <button
           onClick={handleDecrement}
           disabled={isLoading}
           aria-label="Decrease quantity"
-          className="p-1 hover:bg-black border border-transparent hover:border-border text-secondary hover:text-primary transition-colors disabled:opacity-50 disabled:cursor-not-allowed"
+          className="p-1 hover:bg-surface-container-lowest border border-transparent hover:border-border text-secondary hover:text-primary transition-colors disabled:opacity-50 disabled:cursor-not-allowed"
         >
           <Minus size={16} />
         </button>
@@ -110,7 +110,7 @@ export default function QuantityDisplay({
           onClick={handleIncrement}
           disabled={isLoading}
           aria-label="Increase quantity"
-          className="p-1 hover:bg-black border border-transparent hover:border-border text-secondary hover:text-primary transition-colors disabled:opacity-50 disabled:cursor-not-allowed"
+          className="p-1 hover:bg-surface-container-lowest border border-transparent hover:border-border text-secondary hover:text-primary transition-colors disabled:opacity-50 disabled:cursor-not-allowed"
         >
           <Plus size={16} />
         </button>
@@ -123,7 +123,7 @@ export default function QuantityDisplay({
       onClick={handleTapToEdit}
       disabled={isLoading}
       aria-label={`Quantity: ${currentQuantity}. Tap to edit`}
-      className="text-lg font-normal text-primary hover:bg-black border border-transparent hover:border-border px-3 py-2 transition-colors disabled:opacity-50 disabled:cursor-not-allowed"
+      className="text-lg font-normal text-primary hover:bg-surface-container-lowest border border-transparent hover:border-border px-3 py-2 transition-colors disabled:opacity-50 disabled:cursor-not-allowed"
     >
       {currentQuantity}
     </button>