feat(creator-studio): two-row masthead with site logo and user avatar

顶栏改为知乎式两行结构：第一行左侧站点 LOGO、右侧当前用户头像，
第二行只保留正文工具条并居中，同时移除「Jio / 写文章」字样。

- bootstrap payload 新增 site/viewer 身份字段（复用 jio_get_site_logo_url
  与 jio_get_avatar_url，前端不拼 URL、不做权限判断）
- 拆分 draft 类型、TinyMCE 块运行时、顶栏组件，index.tsx 1065 → 735 行
- 清理死代码：未调用的 keepCaretInsideCode、永远无法打开的代码语言弹窗
  （setCodeLanguage 只会收到 null，codeTargetRef 从未赋值）及其样式，
  以及顶栏移除后失效的 bar-left/brand/mode/save-draft/ghost/primary 规则
- 契约测试、本地预览与截图脚本同步到新 DOM

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

assets/creator-studio/scripts/smoke.cjs

@@ -74,12 +74,14 @@ if (!EDGE) {
   await new Promise((r) => setTimeout(r, 3000));
 
   const state = await page.evaluate(() => ({
+    hasMasthead: !!document.querySelector('.jio-creator__masthead'),
+    hasBrandLogo: !!document.querySelector('.jio-creator__brand-logo'),
+    hasAvatar: !!document.querySelector('.jio-creator__me-avatar'),
     hasBar: !!document.querySelector('.jio-creator__bar'),
     hasToolbar: !!document.querySelector('.jio-creator__toolbar-tools'),
     hasTinyMce: !!window.tinymce?.get('jio-creator-content'),
     hasEditorFrame: !!document.querySelector('.mce-tinymce iframe, .tox-tinymce iframe'),
     hasTitle: !!document.querySelector('.jio-creator__title textarea'),
-    hasSaveDraft: !!document.querySelector('.jio-creator__save-draft'),
     toolbarActions: Array.from(document.querySelectorAll('.jio-creator__toolbar-tools button')).map((button) => button.getAttribute('aria-label') || button.textContent.trim()),
     saveText: (document.querySelector('.jio-creator__save') || {}).textContent,
     rejections: window.__jioRejections || [],