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

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

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

@@ -66,6 +66,19 @@ test('stale autosave requests are rejected instead of overwriting', () => {
 	assert.match(appSource, /status === 409/);
 });
 
+test('drafts save with partial content instead of being rejected', () => {
+	// 只写标题、或正文只有图片/表格/代码块时，也必须能存草稿。
+	assert.match(saveTrait, /请先写点什么再保存/);
+	const draftBranch = saveTrait.indexOf('if (!$is_draft) {');
+	const titleGuard = saveTrait.indexOf("if ($title === '') {");
+	assert.ok(draftBranch !== -1 && titleGuard !== -1, 'draft branch and title guard both exist');
+	assert.ok(draftBranch < titleGuard, 'title/content requirements only apply to submit');
+	// 前端空文档不再发保存请求。
+	assert.match(appSource, /const hasDocument = /);
+	assert.match(appSource, /if \(!hasDocument\) \{\s*return true;/);
+	assert.match(appSource, /img\|table\|pre\|hr\|iframe\|video/);
+});
+
 test('paid payload is validated before any post write', () => {
 	const prepareAt = saveTrait.indexOf('prepare_pay_meta');
 	const insertAt = saveTrait.indexOf('wp_insert_post');