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_data2.js

@@ -0,0 +1,21 @@
+const { chromium } = require('playwright');
+(async () => {
+  const browser = await chromium.launch({ headless: true });
+  const page = await (await browser.newContext({viewport:{width:1280,height:900}})).newPage();
+  const logs = [];
+  page.on('console', m => logs.push(m.text()));
+  page.on('pageerror', e => logs.push('PAGEERR: ' + e.message));
+  await page.goto('http://127.0.0.1:8099/buy-service/1/pos', { waitUntil: 'load' }).catch(()=>{});
+  await page.waitForTimeout(7000);
+  // 找 data 打印 + RangeError
+  const dataLog = logs.find(l => l.startsWith('data:'));
+  console.log('=== data ===', dataLog ? dataLog.slice(0,400) : '(无)');
+  // 看 service_selections / options 部分
+  if (dataLog) {
+    const m = dataLog.match(/service_selections:[^,}]+/);
+    if (m) console.log('service_selections:', m[0].slice(0,200));
+    const o = dataLog.match(/options:[^]]*\]/);
+    if (o) console.log('options:', o[0].slice(0,200));
+  }
+  await browser.close();
+})();