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/dump_idb.js

@@ -0,0 +1,47 @@
+// dump IndexedDB 结构 + Hive entry 格式
+const { chromium } = require('playwright');
+const BASE = 'http://127.0.0.1:8099';
+(async () => {
+  const browser = await chromium.launch({ headless: true });
+  const page = await (await browser.newContext()).newPage();
+  await page.goto(BASE + '/', { waitUntil: 'load', timeout: 60000 });
+  await page.waitForTimeout(7000);
+
+  const result = await page.evaluate(async () => {
+    const out = {};
+    const dbs = await indexedDB.databases();
+    out.databases = dbs.map(d => d.name);
+    for (const db of dbs) {
+      out[db.name] = [];
+      await new Promise((resolve) => {
+        const req = indexedDB.open(db.name);
+        req.onsuccess = () => {
+          const d = req.result;
+          const stores = [...d.objectStoreNames];
+          out[db.name + '_stores'] = stores;
+          if (stores.length === 0) { d.close(); resolve(); return; }
+          const tx = d.transaction(stores[0], 'readonly');
+          const store = tx.objectStore(stores[0]);
+          const allReq = store.getAll();
+          const keysReq = store.getAllKeys();
+          allReq.onsuccess = () => {
+            out[db.name] = allReq.result.map((v, i) => {
+              let hex = '';
+              if (v instanceof ArrayBuffer) {
+                const u = new Uint8Array(v);
+                hex = Array.from(u.slice(0, 40)).map(b => b.toString(16).padStart(2,'0')).join(' ');
+                return { key: keysReq.result[i], valueBytes: v.byteLength, hexFirst40: hex };
+              }
+              return { key: keysReq.result[i], value: typeof v === 'string' ? v.slice(0,80) : v };
+            });
+          };
+          tx.oncomplete = () => { d.close(); resolve(); };
+        };
+        req.onerror = () => resolve();
+      });
+    }
+    return out;
+  });
+  console.log(JSON.stringify(result, null, 2));
+  await browser.close();
+})().catch(e => { console.error('失败:', e.message); process.exit(1); });