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>

tests/widget-system/creator-studio-contract.test.cjs

@@ -214,7 +214,8 @@ test('fixed top toolbar has TinyMCE formatting, media, and extension actions', (
 	assert.match(blocks, /function append_footnotes/);
 	assert.match(blocks, /<sup>\$1\$2<\/sup>/);
 	// 删除键必须能移除相邻的块级元素。
-	assert.match(appSource, /function removeAdjacentBlock/);
+	const editorRuntime = read('assets/creator-studio/src/editor-runtime.ts');
+	assert.match(editorRuntime, /function removeAdjacentBlock/);
 	assert.match(appSource, /removeAdjacentBlock\(editor, event\)/);
 	// 工具栏按钮统一为「图标在上、文字在下」。
 	assert.match(editorToolbar, /jio-creator__tool-label/);
@@ -231,8 +232,37 @@ test('fixed top toolbar has TinyMCE formatting, media, and extension actions', (
 	assert.match(barStyles, /\.jio-creator__status\s*\{[\s\S]*?position:\s*fixed/);
 	assert.match(barStyles, /\.jio-creator__status\s*\{[\s\S]*?bottom:\s*0/);
 	assert.match(editorToolbar, /role="toolbar"/);
-	assert.match(read('assets/creator-studio/src/styles/studio.scss'), /\.jio-creator__bar\s*\{[^}]*position:\s*fixed/);
-	assert.match(read('assets/creator-studio/src/styles/studio.scss'), /\.jio-creator\s*\{[\s\S]*?padding-top:\s*var\(--jc-bar\)/);
+	assert.match(read('assets/creator-studio/src/styles/studio.scss'), /\.jio-creator__top\s*\{[^}]*position:\s*fixed/);
+	assert.match(read('assets/creator-studio/src/styles/studio.scss'), /\.jio-creator\s*\{[\s\S]*?padding-top:\s*var\(--jc-top\)/);
+});
+
+test('top bar is masthead + centered toolbar, with no brand text in the toolbar row', () => {
+	const masthead = read('assets/creator-studio/src/components/studio-masthead.tsx');
+	const styles = read('assets/creator-studio/src/styles/studio.scss');
+	const rest = read('src/Core/CreatorRest.php');
+
+	// 第一行：左站点 LOGO、右用户头像。
+	assert.match(appSource, /<StudioMasthead/);
+	assert.match(masthead, /jio-creator__masthead/);
+	assert.match(masthead, /jio-creator__brand-logo/);
+	assert.match(masthead, /jio-creator__me-avatar/);
+	assert.match(masthead, /site\.logo/);
+	assert.match(masthead, /viewer\.avatar/);
+	// 工具条行不再有品牌字 / 模式文案。
+	assert.doesNotMatch(appSource, /jio-creator__bar-brand/);
+	assert.doesNotMatch(appSource, /jio-creator__bar-mode/);
+	assert.doesNotMatch(appSource, /jio-creator__bar-left/);
+	// 工具条居中。
+	assert.match(styles, /\.jio-creator__bar\s*\{[^}]*justify-content:\s*center/);
+	// Logo 与头像由服务端 bootstrap 提供，不在前端拼 URL。
+	assert.match(rest, /private function identity_payload/);
+	assert.match(rest, /'site'\s*=>\s*\$ident\['site'\]/);
+	assert.match(rest, /'viewer'\s*=>\s*\$ident\['viewer'\]/);
+	assert.match(rest, /jio_get_site_logo_url/);
+	assert.match(rest, /jio_get_avatar_url/);
+	// 顶栏身份字段与前端读取保持一致，避免悬空字段。
+	assert.doesNotMatch(read('assets/creator-studio/src/components/studio-masthead.tsx'), /viewer\.home/);
+	assert.doesNotMatch(rest, /'home'\s*=>\s*esc_url_raw\(\$home\)/);
 });
 
 test('creator studio build artifacts and contracts exist', () => {