feat(creator-studio): centered paper layout and scheduled publishing

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

assets/creator-studio/scripts/preview.cjs

@@ -63,10 +63,11 @@ const mockBootstrap = {
     canPay: true,
     canPayDownload: true,
     canPublishNow: true,
+    canSchedule: true,
     canEdit: true,
     isLoggedIn: true,
   },
-  limits: { titleMin: 5, titleMax: 30, titlePlaceholder: '请输入标题', contentPlaceholder: '开始写作…' },
+  limits: { titleMin: 5, titleMax: 100, titlePlaceholder: '请输入标题', contentPlaceholder: '请输入正文' },
   author: { name: '预览作者', avatar: '', meta: '' },
   privateUploads: [],
   privateStorage: false,
@@ -82,6 +83,7 @@ const mockBootstrap = {
     bootstrapUrl: '#',
   },
   nonce: 'preview',
+  timezone: 'Asia/Shanghai',
 };
 
 // 换成模拟数据。WP 的 wp_add_inline_script 会在结尾追加 sourceURL 注释，