feat: 集成支付宝电脑网站支付（alipay direct）

- 新增 src/lib/alipay/ 模块：RSA2 签名、网关客户端、AlipayProvider
- 新增 /api/alipay/notify 异步通知回调路由
- config.ts 添加 ALIPAY_* 环境变量
- payment/index.ts 注册 alipaydirect 提供商
- 27 个单元测试全部通过

src/lib/alipay/client.ts

@@ -0,0 +1,100 @@
+import { getEnv } from '@/lib/config';
+import { generateSign } from './sign';
+import type { AlipayResponse } from './types';
+
+const GATEWAY = 'https://openapi.alipay.com/gateway.do';
+
+function getCommonParams(appId: string): Record<string, string> {
+  return {
+    app_id: appId,
+    format: 'JSON',
+    charset: 'utf-8',
+    sign_type: 'RSA2',
+    timestamp: new Date().toISOString().replace('T', ' ').substring(0, 19),
+    version: '1.0',
+  };
+}
+
+function assertAlipayEnv(env: ReturnType<typeof getEnv>) {
+  if (!env.ALIPAY_APP_ID || !env.ALIPAY_PRIVATE_KEY || !env.ALIPAY_PUBLIC_KEY) {
+    throw new Error(
+      'Alipay environment variables (ALIPAY_APP_ID, ALIPAY_PRIVATE_KEY, ALIPAY_PUBLIC_KEY) are required',
+    );
+  }
+  return env as typeof env & {
+    ALIPAY_APP_ID: string;
+    ALIPAY_PRIVATE_KEY: string;
+    ALIPAY_PUBLIC_KEY: string;
+  };
+}
+
+/**
+ * 生成电脑网站支付的跳转 URL（GET 方式）
+ * 用于 alipay.trade.page.pay
+ */
+export function pageExecute(
+  bizContent: Record<string, unknown>,
+  options?: { notifyUrl?: string; returnUrl?: string },
+): string {
+  const env = assertAlipayEnv(getEnv());
+
+  const params: Record<string, string> = {
+    ...getCommonParams(env.ALIPAY_APP_ID),
+    method: 'alipay.trade.page.pay',
+    biz_content: JSON.stringify(bizContent),
+  };
+
+  if (options?.notifyUrl || env.ALIPAY_NOTIFY_URL) {
+    params.notify_url = (options?.notifyUrl || env.ALIPAY_NOTIFY_URL)!;
+  }
+  if (options?.returnUrl || env.ALIPAY_RETURN_URL) {
+    params.return_url = (options?.returnUrl || env.ALIPAY_RETURN_URL)!;
+  }
+
+  params.sign = generateSign(params, env.ALIPAY_PRIVATE_KEY);
+
+  const query = new URLSearchParams({ ...params, sign_type: 'RSA2' }).toString();
+  return `${GATEWAY}?${query}`;
+}
+
+/**
+ * 调用支付宝服务端 API（POST 方式）
+ * 用于 alipay.trade.query、alipay.trade.refund、alipay.trade.close
+ */
+export async function execute<T extends AlipayResponse>(
+  method: string,
+  bizContent: Record<string, unknown>,
+): Promise<T> {
+  const env = assertAlipayEnv(getEnv());
+
+  const params: Record<string, string> = {
+    ...getCommonParams(env.ALIPAY_APP_ID),
+    method,
+    biz_content: JSON.stringify(bizContent),
+  };
+
+  params.sign = generateSign(params, env.ALIPAY_PRIVATE_KEY);
+  params.sign_type = 'RSA2';
+
+  const response = await fetch(GATEWAY, {
+    method: 'POST',
+    headers: { 'Content-Type': 'application/x-www-form-urlencoded' },
+    body: new URLSearchParams(params).toString(),
+  });
+
+  const data = await response.json();
+
+  // 支付宝响应格式：{ "alipay_trade_query_response": { ... }, "sign": "..." }
+  const responseKey = method.replace(/\./g, '_') + '_response';
+  const result = data[responseKey] as T;
+
+  if (!result) {
+    throw new Error(`Alipay API error: unexpected response format for ${method}`);
+  }
+
+  if (result.code !== '10000') {
+    throw new Error(`Alipay API error: [${result.sub_code || result.code}] ${result.sub_msg || result.msg}`);
+  }
+
+  return result;
+}