fix: admin pages CSS variables - consistent design system colors

src/app/admin/products/[id]/page.tsx

@@ -30,7 +30,7 @@ export default async function ProductDetailPage({ params }: ProductDetailPagePro
 
   if (error || !product) {
     return (
-      <main className="min-h-screen bg-stone-100 px-6 py-12">
+      <main className="min-h-screen px-6 py-12" style={{ backgroundColor: "var(--admin-bg)" }}>
         <div className="mx-auto max-w-4xl">
           <h1 className="text-3xl font-bold text-red-600">Product not found</h1>
           <pre className="mt-4 rounded-xl bg-white p-4 text-sm text-stone-600">
@@ -48,7 +48,7 @@ export default async function ProductDetailPage({ params }: ProductDetailPagePro
   }
 
   return (
-    <main className="min-h-screen bg-stone-100 px-6 py-12">
+    <main className="min-h-screen px-6 py-12" style={{ backgroundColor: "var(--admin-bg)" }}>
       <div className="mx-auto max-w-4xl">
         <a
           href="/admin/products"

src/app/admin/products/import/page.tsx

@@ -81,7 +81,7 @@ Citrus Gift Box,Seasonal citrus assortment,34.99,Shipping,TRUE,
   }
 
   return (
-    <main className="min-h-screen bg-stone-100 px-6 py-10">
+    <main className="min-h-screen px-6 py-10" style={{ backgroundColor: "var(--admin-bg)" }}>
       <div className="mx-auto max-w-4xl">
         <div className="mb-6 flex items-center justify-between">
           <div>

src/app/admin/products/new/page.tsx

@@ -6,7 +6,7 @@ export default async function NewProductPage() {
   const adminUser = await getAdminUser();
   if (!adminUser?.can_manage_products) redirect("/admin/pickup");
   return (
-    <main className="min-h-screen bg-stone-100 px-6 py-12">
+    <main className="min-h-screen px-6 py-12" style={{ backgroundColor: "var(--admin-bg)" }}>
       <div className="mx-auto max-w-4xl">
         <div className="mb-8">
           <a