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/app/admin/advanced/page.tsx

@@ -3,6 +3,7 @@ import { getAdminUser } from "@/lib/admin-permissions";
 import { getBrands } from "@/actions/admin/users";
 import { getStripeConnectStatus } from "@/actions/stripe-connect";
 import AdvancedSettingsClient from "@/components/admin/AdvancedSettingsClient";
+import { PageHeader } from "@/components/admin/design-system";
 
 export const metadata = {
   title: "Advanced Settings - Route Commerce Admin",
@@ -25,10 +26,28 @@ export default async function AdvancedSettingsPage() {
   const stripeConnect = brandId ? await getStripeConnectStatus(brandId) : null;
 
   return (
-    <AdvancedSettingsClient
-      brandId={brandId}
-      brands={brands}
-      stripeConnect={stripeConnect}
-    />
+    <main className="min-h-screen bg-[var(--admin-bg)] px-6 py-10">
+      <div className="mx-auto max-w-4xl">
+        <PageHeader
+          breadcrumb={[
+            { label: "Admin", href: "/admin" },
+            { label: "Settings", href: "/admin/settings" },
+            { label: "Advanced" },
+          ]}
+          title="Advanced Settings"
+          subtitle="Developer settings, APIs, and integrations"
+          icon={
+            <svg className="h-6 w-6" viewBox="0 0 24 24" fill="none" stroke="currentColor" strokeWidth="2" strokeLinecap="round" strokeLinejoin="round">
+              <path d="M9.813 15.904L9 18.75l-.813-2.846a4.5 4.5 0 00-3.09-3.09L2.25 12l2.846-.813a4.5 4.5 0 003.09-3.09L9 5.25l.813 2.846a4.5 4.5 0 003.09 3.09L15.75 12l-2.846.813a4.5 4.5 0 00-3.09 3.09zM18.259 8.715L18 9.75l-.259-1.035a3.375 3.375 0 00-2.455-2.456L14.25 6l1.036-.259a3.375 3.375 0 002.455-2.456L18 2.25l.259 1.035a3.375 3.375 0 002.456 2.456L21.75 6l-1.035.259a3.375 3.375 0 00-2.456 2.456zM16.894 20.567L16.5 21.75l-.394-1.183a2.25 2.25 0 00-1.423-1.423L13.5 18.75l1.183-.394a2.25 2.25 0 001.423-1.423l.394-1.183.394 1.183a2.25 2.25 0 001.423 1.423l1.183.394-1.183.394a2.25 2.25 0 00-1.423 1.423z"/>
+            </svg>
+          }
+        />
+        <AdvancedSettingsClient
+          brandId={brandId}
+          brands={brands}
+          stripeConnect={stripeConnect}
+        />
+      </div>
+    </main>
   );
 }