fix(creator-studio): 固定公众号式创作工具栏

- 顶部改为 fixed 创作工具栏：左侧返回/品牌/模式，中间文章标题与保存状态，
  右侧撤销/重做、保存草稿、预览、发布
- 新增工作台级撤销/重做快照栈，连续编辑合并记录；支持 Ctrl/Cmd+Z / Shift+Z，
  不覆盖 RichText 输入框自身的编辑历史
- 移动端收敛工具栏布局，保留撤销/重做、预览、发布
- 先保存草稿再请求审核/直接发布；请求使用服务端更新后的文章与版本 ID
- 固定工具栏以独立 chrome 层布局，正文避开顶部工具栏高度
- 补充固定工具栏、历史操作与键盘快捷键契约

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

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

@@ -132,6 +132,19 @@ test('studio app keeps autosave, recovery, and the publish drawer wired', () =>
 	assert.match(drawer, /立即发布/);
 });
 
+test('固定顶栏包含保存状态、撤销/重做、预览和发布动作', () => {
+	assert.match(appSource, /className="jio-creator__bar"/);
+	assert.match(appSource, /history\.undo\(\)/);
+	assert.match(appSource, /history\.redo\(\)/);
+	assert.match(appSource, /保存草稿/);
+	assert.match(appSource, /<SaveState value=\{saveState\}/);
+	assert.match(appSource, /draftRef\.current\.postId/);
+	assert.match(appSource, /useEditorHistory/);
+	assert.match(appSource, /event\.shiftKey \? redo\(\) : undo\(\)/);
+	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\(--jc-bar\)/);
+});
+
 test('creator studio build artifacts and contracts exist', () => {
 	assert.ok(exists('assets/creator-studio/package.json'));
 	assert.ok(exists('assets/creator-studio/package-lock.json'));