fix(front-submit): let drafts save with partial content

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

assets/creator-studio/src/index.tsx

@@ -459,8 +459,10 @@ function Studio(): JSX.Element {
 				return true;
 			}
 			const requestRevision = editRevisionRef.current;
-			const hasDocument = current.title.trim() !== '' || plainText(current.content).trim() !== '';
-			if (autosave && !hasDocument) {
+			// 空文档（连块级内容都没有）不发请求：服务端会拒绝，前端也不该把它当失败。
+			const hasDocument = current.title.trim() !== '' || plainText(current.content).trim() !== ''
+				|| /<(?:img|table|pre|hr|iframe|video)/i.test(current.content);
+			if (!hasDocument) {
 				return true;
 			}
 			setSaveState({ state: 'saving', at: '' });