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/admin/CategoryManager.tsx

@@ -60,7 +60,7 @@ export default function CategoryManager({
                 <button
                   onClick={() => onDeleteCategory(cat.id, cat.name)}
                   data-testid="delete-category-button"
-                  className="p-2 text-secondary hover:text-rose-500 hover:bg-rose-500/5 transition-all"
+                  className="p-2 text-secondary hover:text-error hover:bg-error/5 transition-all"
                 >
                   <Trash2 size={14} />
                 </button>