feat(admin): 제품 관리 — CRUD + 파일 업로드·제품 배정

Co-Authored-By: Claude Sonnet 4.6 <noreply@anthropic.com>

app/admin/components/AdminSidebar.tsx

@@ -46,6 +46,16 @@ const NAV_ITEMS = [
       </svg>
     ),
   },
+  {
+    href: '/admin/products',
+    label: '제품 관리',
+    icon: (
+      <svg className="w-5 h-5" fill="none" stroke="currentColor" viewBox="0 0 24 24">
+        <path strokeLinecap="round" strokeLinejoin="round" strokeWidth={2}
+          d="M20 7l-8-4-8 4m16 0l-8 4m8-4v10l-8 4m0-10L4 7m8 4v10M4 7v10l8 4" />
+      </svg>
+    ),
+  },
   {
     href: '/admin/contacts',
     label: '문의 내역',