feat(admin): 品牌管理 + 新建商品

品牌管理：列出品牌及引用商品数，支持改名、合并重复品牌（把源品牌的商品并入目标后删除源）、删除未被引用的品牌。新建商品：商品列表新增「新建商品」入口，填写名称/条码/品牌/品类后创建并进入详情页继续补全。

Co-Authored-By: Devin AI <158243242+devin-ai-integration[bot]@users.noreply.github.com>

admin-frontend/src/App.tsx

@@ -6,9 +6,10 @@ import ProductDetail from "./components/ProductDetail";
 import SubmissionsPage from "./components/SubmissionsPage";
 import ApiKeysPage from "./components/ApiKeysPage";
 import CategoriesPage from "./components/CategoriesPage";
-import { FolderTree, Inbox, KeyRound, LogOut, Package } from "lucide-react";
+import BrandsPage from "./components/BrandsPage";
+import { FolderTree, Inbox, KeyRound, LogOut, Package, Tag } from "lucide-react";
 
-type Tab = "products" | "submissions" | "categories" | "keys";
+type Tab = "products" | "submissions" | "categories" | "brands" | "keys";
 type View = { name: "list" } | { name: "detail"; id: string };
 
 export default function App() {
@@ -114,6 +115,16 @@ export default function App() {
             >
               <FolderTree className="h-4 w-4" /> 分类管理
             </button>
+            <button
+              onClick={() => setTab("brands")}
+              className={`px-3 py-1.5 rounded-md flex items-center gap-1.5 ${
+                tab === "brands"
+                  ? "bg-emerald-50 text-emerald-700"
+                  : "text-gray-600 hover:bg-gray-100"
+              }`}
+            >
+              <Tag className="h-4 w-4" /> 品牌管理
+            </button>
             <button
               onClick={() => setTab("keys")}
               className={`px-3 py-1.5 rounded-md flex items-center gap-1.5 ${
@@ -141,6 +152,8 @@ export default function App() {
           <ApiKeysPage />
         ) : tab === "categories" ? (
           <CategoriesPage />
+        ) : tab === "brands" ? (
+          <BrandsPage />
         ) : tab === "submissions" ? (
           <SubmissionsPage onPending={setPending} />
         ) : view.name === "list" ? (