feat(creator-studio): 图片宽度四档与作者行

- 通过 editor.BlockEdit 过滤器给 core/image 增加「半屏 / 中等 / 通栏 / 全宽」
  四档宽度，选中图片时出现在区块工具条；宽度写入 className 并序列化到
  post_content，前台样式即可生效，无需自定义区块或额外元数据
- 前台样式：半屏靠左 50%，中等 72%，通栏跟随正文行宽，全宽突破行宽但受容器
  内边距约束；移动端半屏与全宽回退为整行，避免横向滚动
- 新增作者行（头像 + 昵称 + 身份说明），数据由 CreatorRest::author_payload()
  从服务端给出，前端不自行拼装；无昵称时整行不渲染，头像缺失时回退首字占位
- 作者行放在摘要之后、正文之前

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

assets/creator-studio/src/index.tsx

@@ -19,8 +19,10 @@ import { __ } from '@wordpress/i18n';
 import { apiPost } from './services/api';
 import { installApiFetchNonce } from './services/api-fetch';
 import { installMediaUploadBridge } from './services/media';
+import { installImageWidthPresets } from './extensions/image-width';
 import { PublishDrawer } from './panels/publish-drawer';
 import { CoverStrip } from './components/cover-strip';
+import { AuthorRow } from './components/author-row';
 import { InsertPanel, type InsertItem } from './panels/insert-panel';
 import { buildInsertGroups } from './utils/insert-items';
 import { SaveState, type SaveStateValue } from './components/save-state';
@@ -420,6 +422,8 @@ function Studio(): JSX.Element {
 					/>
 				</label>
 
+				<AuthorRow author={bootstrap.author || {}} />
+
 				<div className="jio-creator__editor">
 					<BlockEditorProvider
 						value={blocks}
@@ -497,6 +501,7 @@ function mount() {
 	}
 	installApiFetchNonce(nonce);
 	installMediaUploadBridge(bootstrap, nonce);
+	installImageWidthPresets();
 	target.classList.add('is-ready');
 	createRoot(target).render(<Studio />);
 }