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>

src/Core/CreatorRest.php

@@ -127,7 +127,9 @@ final class CreatorRest {
 			? (array) get_post_meta($source->ID, DomainModel::POST_META_KEY, true)
 			: [];
 
-		$terms = $this->term_payload($settings, $source, $snapshot);
+		$terms  = $this->term_payload($settings, $source, $snapshot);
+		$viewer = $user_id > 0 ? get_userdata($user_id) : null;
+		$ident  = $this->identity_payload($viewer instanceof \WP_User ? $viewer : null);
 
 		return [
 			'sourceId'   => $post_id,
@@ -172,6 +174,40 @@ final class CreatorRest {
 				'newPost'  => function_exists('jio_get_new_post_url') ? jio_get_new_post_url() : '',
 				'center'   => function_exists('jio_get_user_center_url') ? jio_get_user_center_url('posts') : '',
 			],
+			'site'       => $ident['site'],
+			'viewer'     => $ident['viewer'],
+		];
+	}
+
+	/**
+	 * 顶栏身份信息：站点 Logo 与当前用户头像。
+	 *
+	 * 只做展示，不承载权限判断；Logo 缺失时前端回退到品牌文字。
+	 *
+	 * @return array{site: array<string, string>, viewer: array<string, string>}
+	 */
+	private function identity_payload(?\WP_User $viewer = null): array {
+		$brand = function_exists('jio_get_site_logo_text') ? (string) jio_get_site_logo_text() : '';
+		$brand = $brand !== '' ? $brand : (string) get_bloginfo('name');
+
+		$logo = function_exists('jio_get_site_logo_url') ? trim((string) jio_get_site_logo_url()) : '';
+		if ($logo === '') {
+			$logo = get_template_directory_uri() . '/assets/img/logo.png';
+		}
+
+		$avatar = $viewer instanceof \WP_User && function_exists('jio_get_avatar_url')
+			? (string) jio_get_avatar_url($viewer, ['size' => 72])
+			: '';
+
+		return [
+			'site'   => [
+				'home' => esc_url_raw(home_url('/')),
+				'name' => $brand,
+				'logo' => esc_url_raw($logo),
+			],
+			'viewer' => [
+				'avatar' => esc_url_raw($avatar),
+			],
 		];
 	}