feat(admin): design system audit fixes

- Add CSS design tokens for consistency (--admin-danger-hover, --admin-accent-dot, shadow-md warm tone)
- Replace unicode icons with inline SVG (⋮, ✕, ▼, ▶)
- Consolidate duplicate PageHeader/AdminPageHeader components
- Standardize border-radius (rounded-xl → rounded-lg for ViewModeTabs)
- Remove hardcoded brand UUID in products page
- Replace hardcoded bg-red-600 with CSS variables in delete buttons
- Add AdminButton, AdminFilterTabs, AdminSearchInput, PageHeader design system components
- Fix GlassModal and AdminModal close button styling
- Remove duplicate 'New Lot' button on Route Trace dashboard

src/components/admin/design-system/AdminModal.tsx

@@ -33,7 +33,7 @@ export default function AdminModal({ title, subtitle, onClose, children, maxWidt
       <div
         className={`relative w-full ${maxWidth} rounded-2xl`}
         style={{
-          backgroundColor: "#ffffff",
+          backgroundColor: "var(--admin-card-bg)",
           border: "1px solid var(--admin-border)",
           boxShadow: "0 25px 50px -12px rgba(60, 56, 37, 0.35), 0 12px 24px -8px rgba(60, 56, 37, 0.2)",
         }}