feat: add products/cases pages and lead-capture form block

- types: Product/CaseStudy page types, CaseStudyBlockValue, FormBlockValue
- services: product.service.ts, case.service.ts
- app/products, app/cases: list + detail pages
- blocks: CaseStudyCard, LeadForm (submits to /api/v1/custom/leads/)
- Header nav: add 产品/案例 links

app/products/page.tsx

@@ -0,0 +1,35 @@
+import Link from "next/link";
+import type { Metadata } from "next";
+import { getProductList } from "@/services/product.service";
+
+export const metadata: Metadata = {
+  title: "产品",
+};
+
+export default async function ProductListPage() {
+  const products = await getProductList().catch(() => []);
+
+  return (
+    <div className="mx-auto max-w-4xl px-6 py-24">
+      <h1 className="mb-12 text-4xl font-bold text-slate-900">产品</h1>
+      <ul className="space-y-6">
+        {products.map((product) => (
+          <li key={product.id} className="border-b border-slate-100 pb-6">
+            <Link
+              href={`/products/${product.meta.slug}`}
+              className="text-2xl font-semibold text-slate-900 hover:text-primary"
+            >
+              {product.title}
+            </Link>
+            {product.summary && (
+              <p className="mt-2 text-slate-600">{product.summary}</p>
+            )}
+          </li>
+        ))}
+        {products.length === 0 && (
+          <p className="text-slate-500">暂无产品，或后端服务未连接。</p>
+        )}
+      </ul>
+    </div>
+  );
+}