feat(ecommerce): 电商模板改为从服务端 API 加载

- 新增 ecommerceTemplateClient，通过应用 API 拉取模板清单（符合 AGENTS.md 数据走 API 规则）
- EcommercePage 接入远程模板，按 categorySlug 映射到场景，补充 mediaType/sourceAssets
- 移除硬编码 popularCommerceScenarioTemplates，改为远程模板为空时回退本地
- 补充 ecommerce-standalone.css 模板条样式
- .gitignore 忽略 ecommerce-template-manifest.* 运行时清单（属 API/OSS 数据，不入库）

src/api/ecommerceTemplateClient.ts

@@ -0,0 +1,58 @@
+import { serverRequest } from "./serverConnection";
+
+export interface EcommerceTemplateAsset {
+  fileName?: string;
+  extension?: string;
+  sizeBytes?: number;
+  assetIndex?: number;
+  ossKey?: string;
+  url?: string;
+}
+
+export interface EcommerceTemplatePreview {
+  fileName?: string;
+  extension?: string;
+  sizeBytes?: number;
+  ossKey?: string;
+  url?: string;
+}
+
+export interface EcommerceTemplateManifestItem {
+  id: string;
+  category?: string;
+  categorySlug?: string;
+  templateName?: string;
+  templateSlug?: string;
+  preview?: EcommerceTemplatePreview;
+  prompt?: string;
+  assets?: EcommerceTemplateAsset[];
+}
+
+export interface EcommerceTemplateListResult {
+  version?: number;
+  ossPrefix?: string;
+  generatedAt?: string;
+  templates: EcommerceTemplateManifestItem[];
+  total: number;
+}
+
+export async function listEcommerceTemplates(category?: string): Promise<EcommerceTemplateListResult> {
+  const search = new URLSearchParams();
+  if (category) search.set("category", category);
+  const suffix = search.toString();
+
+  const response = await serverRequest<EcommerceTemplateListResult>(
+    `ai/ecommerce/templates${suffix ? `?${suffix}` : ""}`,
+    {
+      method: "GET",
+      maxRetries: 1,
+      fallbackMessage: "Failed to load ecommerce templates",
+    },
+  );
+
+  return {
+    ...response,
+    templates: Array.isArray(response.templates) ? response.templates : [],
+    total: Number.isFinite(response.total) ? response.total : Array.isArray(response.templates) ? response.templates.length : 0,
+  };
+}