fix(runtime): e2e 发现的 3 个 bug 修复

- download: desktop_download_apps SingleChildScrollView 加 primary:true (Scrollbar 缺 ScrollPosition)
- contact-stores: checkDomainAvailability async 后 setState 加 mounted 保护 (dispose 后 setState)
- buy-service: _loadData 加 data 结构校验 + mounted 保护 (API 400 无效参数时 data 为错误结构 -> RangeError)

tools/e2e/capture_api.js

@@ -0,0 +1,22 @@
+// 拦截 buy-service 的 API 请求/响应，看实际数据结构
+const { chromium } = require('playwright');
+(async () => {
+  const browser = await chromium.launch({ headless: true });
+  const page = await (await browser.newContext({viewport:{width:1280,height:900}})).newPage();
+  page.on('response', async (resp) => {
+    const url = resp.url();
+    if (url.includes('get-buy-service-info')) {
+      console.log('=== buy-service API 响应 ===');
+      console.log('状态:', resp.status());
+      try {
+        const body = await resp.text();
+        console.log('body:', body.slice(0, 700));
+      } catch(e) { console.log('读 body 失败'); }
+    }
+  });
+  page.on('pageerror', e => console.log('PAGEERR:', e.message.slice(0,150)));
+  page.on('console', m => { if (m.text().startsWith('data:') || m.text().includes('RangeError')) console.log('CONSOLE:', m.text().slice(0,200)); });
+  await page.goto('http://127.0.0.1:8099/buy-service/1/pos', { waitUntil: 'load' }).catch(()=>{});
+  await page.waitForTimeout(8000);
+  await browser.close();
+})();