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/diag2.js

@@ -0,0 +1,32 @@
+// 诊断 v2：打印完整 CK_STACK（定位 framework 抛的错误的源头）
+const { chromium } = require('playwright');
+const BASE = 'http://127.0.0.1:8099';
+const ROUTES = ['/buy-service/1/pos', '/download'];
+
+(async () => {
+  const browser = await chromium.launch({ headless: true });
+  for (const route of ROUTES) {
+    const ctx = await browser.newContext({ viewport: { width: 1280, height: 900 } });
+    const page = await ctx.newPage();
+    const allLogs = [];
+    page.on('pageerror', e => allLogs.push(`PAGEERROR: ${e.stack || e.message}`));
+    page.on('console', m => allLogs.push(m.text()));
+    await page.goto(BASE + route, { waitUntil: 'load', timeout: 30000 }).catch(()=>{});
+    await page.waitForTimeout(5000);
+
+    console.log(`\n########## ${route} ##########`);
+    for (let i = 0; i < allLogs.length; i++) {
+      const l = allLogs[i];
+      if (l.startsWith('CK_ERROR:') || l.startsWith('PAGEERROR')) {
+        console.log('--- ' + l.slice(0, 150));
+        if (allLogs[i+1] && allLogs[i+1].startsWith('CK_STACK:')) {
+          // 打印堆栈里所有 flutter_wisetronic 帧
+          const proj = allLogs[i+1].match(/flutter_wisetronic\/[^\s]+/g) || [];
+          console.log('   项目帧: ' + (proj.length ? [...new Set(proj)].join('\n            ') : '(无)'));
+        }
+      }
+    }
+    await ctx.close();
+  }
+  await browser.close();
+})();