feat(creator-studio): 公众号式插入面板与封面条

- 新增常驻「添加内容」按钮与插入面板：分组网格列出正文/标题/列表/引用、
  图片/视频/嵌入、代码/分隔线/表格/付费内容；条目不满足能力时不出现在面板里
- 面板支持方向键在网格内移动焦点、Esc 关闭；桌面居中浮层，移动端贴底抽屉并
  留出安全区
- 空文档插入区块时替换初始空白段落，不留空行
- 新增封面条：无封面时给低调入口，有封面时显示 2.35:1 缩略图，悬停出现
  「更换封面」，右上角可移除
- 补充契约测试：头部/页脚/挂件区开关、插入面板真实区块名与能力过滤、
  中文字数口径

Co-Authored-By: Claude Opus 5 (1M context) <noreply@anthropic.com>

assets/creator-studio/scripts/interact.cjs

@@ -0,0 +1,74 @@
+/**
+ * 交互冒烟：验证插入面板能打开、能插入区块，封面条存在，
+ * 并记录无法捕获的 promise 拒绝。
+ */
+const fs = require('fs');
+const puppeteer = require('puppeteer-core');
+
+const CANDIDATES = [
+  process.env.JIO_BROWSER,
+  'C:\\Program Files\\Google\\Chrome\\Application\\chrome.exe',
+  'C:\\Program Files (x86)\\Microsoft\\Edge\\Application\\msedge.exe',
+].filter(Boolean);
+const BROWSER = CANDIDATES.find((p) => fs.existsSync(p));
+const URL = process.argv[2] || 'https://localhost/jio-preview.html';
+
+(async () => {
+  const browser = await puppeteer.launch({
+    executablePath: BROWSER,
+    headless: 'new',
+    ignoreHTTPSErrors: true,
+    args: ['--disable-gpu', '--no-sandbox'],
+  });
+  const page = await browser.newPage();
+  await page.setViewport({ width: 1440, height: 1000 });
+
+  const errors = [];
+  page.on('pageerror', (e) => errors.push('pageerror: ' + e.message));
+
+  await page.goto(URL, { waitUntil: 'networkidle2', timeout: 60000 });
+  await new Promise((r) => setTimeout(r, 2500));
+
+  const before = await page.evaluate(() => ({
+    blocks: document.querySelectorAll('.block-editor-block-list__block').length,
+    hasInsertBtn: !!document.querySelector('.jio-creator__insert'),
+    hasCover: !!document.querySelector('.jio-creator__cover'),
+  }));
+  console.log('BEFORE ' + JSON.stringify(before));
+
+  // 打开插入面板
+  await page.click('.jio-creator__insert');
+  await new Promise((r) => setTimeout(r, 400));
+  const panel = await page.evaluate(() => ({
+    open: !!document.querySelector('.jio-insert__panel'),
+    items: Array.from(document.querySelectorAll('.jio-insert-item__label')).map((n) => n.textContent),
+  }));
+  console.log('PANEL ' + JSON.stringify(panel));
+
+  // 插入「标题」区块
+  const clicked = await page.evaluate(() => {
+    const btn = Array.from(document.querySelectorAll('.jio-insert-item')).find(
+      (b) => (b.textContent || '').includes('标题')
+    );
+    if (!btn) return false;
+    btn.click();
+    return true;
+  });
+  await new Promise((r) => setTimeout(r, 900));
+
+  const after = await page.evaluate(() => ({
+    panelClosed: !document.querySelector('.jio-insert__panel'),
+    blocks: document.querySelectorAll('.block-editor-block-list__block').length,
+    hasHeading: !!document.querySelector('[data-type="core/heading"]'),
+  }));
+  console.log('AFTER ' + JSON.stringify({ clicked, ...after }));
+
+  await page.screenshot({ path: 'C:/Users/Xing/Desktop/WP-Date/data/wordpress/shot-insert.png' });
+
+  if (errors.length) {
+    console.log('--- errors ---');
+    errors.slice(0, 10).forEach((e) => console.log(e));
+  }
+
+  await browser.close();
+})();