feat(promo): generate WeChat mini-program codes on create

Use getwxacodeunlimit with activity id as scene, upload PNG to OSS qrcode/, and show in HQ admin.

Co-authored-by: Cursor <cursoragent@cursor.com>

server/dukang-api/src/integrations/wechat/wechat.mock.provider.ts

@@ -1,9 +1,11 @@
 import { createHash } from 'crypto';
 import { Injectable, NotImplementedException } from '@nestjs/common';
+import * as QRCode from 'qrcode';
 import type {
   IWechatProvider,
   WechatCodeSession,
   WechatOAuthSession,
+  WechatWxaCodeUnlimitedInput,
 } from './wechat.interface';
 
 /**
@@ -81,4 +83,15 @@ export class WechatMockProvider implements IWechatProvider {
   parsePayNotification(): never {
     throw new NotImplementedException('FEATURE_DISABLED');
   }
+
+  /** Mock：用普通二维码 PNG 占位，内容含 scene，便于本地联调上传 OSS */
+  async getWxaCodeUnlimited(input: WechatWxaCodeUnlimitedInput): Promise<Buffer> {
+    const scene = (input.scene ?? '').trim() || 'mock';
+    return QRCode.toBuffer(`mock-wxa://promo?scene=${encodeURIComponent(scene)}`, {
+      width: input.width ?? 430,
+      margin: 1,
+      type: 'png',
+      color: { dark: '#1f1a17', light: '#ffffff' },
+    });
+  }
 }