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/probe2.js

@@ -0,0 +1,51 @@
+// 探测 v2：正确加载 + 截图 + 检测 canvaskit 隐藏 input
+const { chromium } = require('playwright');
+const BASE = 'http://127.0.0.1:8099';
+
+(async () => {
+  const browser = await chromium.launch({ headless: true });
+  const ctx = await browser.newContext({ viewport: { width: 1280, height: 900 } });
+  const page = await ctx.newPage();
+  const logs = [];
+  page.on('pageerror', e => logs.push(`[PAGEERROR] ${e.message.slice(0, 120)}`));
+
+  console.log('=== 访问 /login (load 模式) ===');
+  await page.goto(BASE + '/login', { waitUntil: 'load', timeout: 60000 });
+  await page.waitForTimeout(6000); // 等 Flutter 渲染
+
+  await page.screenshot({ path: 'login.png', fullPage: true });
+  console.log('截图: login.png');
+
+  // 检查所有 input（含 display:none）
+  const inputs = await page.evaluate(() => {
+    return [...document.querySelectorAll('input')].map(e => ({
+      type: e.type,
+      hidden: e.hidden || e.style.display === 'none' || e.offsetParent === null,
+      cls: e.className.slice(0, 50),
+      pos: e.getBoundingClientRect ? (() => { const r = e.getBoundingClientRect(); return {x: Math.round(r.x), y: Math.round(r.y), w: Math.round(r.width), h: Math.round(r.height)}; })() : null,
+    }));
+  });
+  console.log(`所有 input (${inputs.length}):`, JSON.stringify(inputs));
+
+  // 检查 flt-glass-pane 内的 semantics
+  const semTextboxes = await page.locator('[role="textbox"]').count();
+  console.log(`role=textbox: ${semTextboxes}`);
+
+  console.log('\n=== 尝试点击用户名输入框区域，看是否触发 input ===');
+  // canvaskit 点击中间偏上区域（假设用户名框）
+  await page.mouse.click(640, 400);
+  await page.waitForTimeout(1500);
+  const inputsAfterClick = await page.evaluate(() => {
+    return [...document.querySelectorAll('input')].map(e => ({
+      hidden: e.hidden || e.style.display === 'none',
+      pos: (() => { const r = e.getBoundingClientRect(); return {x: Math.round(r.x), y: Math.round(r.y), w: Math.round(r.width)}; })(),
+    }));
+  });
+  console.log('点击后 input:', JSON.stringify(inputsAfterClick));
+  console.log('是否有 activeElement 是 input:', await page.evaluate(() => document.activeElement && document.activeElement.tagName));
+
+  console.log('\n=== pageerror 日志 ===');
+  console.log(logs.slice(0, 5).join('\n'));
+
+  await browser.close();
+})().catch(e => { console.error('失败:', e.message); process.exit(1); });