feat(publish/dongchedi): publish via page context with cover and conservative HTML

懂车帝发布闸现走 Playwright/WebContents 内的 fetch，附带 CSRF token、自动
draft+commit 两步保存，并在前置流程中把正文 HTML 收敛到 p/strong/img、表格
降级为段落、过滤本地素材 URL。同步把懂车帝纳入封面强制平台，更新中英文
提示与错误码文案。

Co-Authored-By: Claude Opus 4.7 (1M context) <noreply@anthropic.com>

apps/admin-web/src/lib/cover-requirements.ts

@@ -33,6 +33,15 @@ const requirementCatalog: Record<string, Partial<PlatformCoverRequirement>> = {
     outputHeight: 800,
     priority: 100,
   },
+  dongchedi: {
+    required: true,
+    supportMode: "native",
+    aspectRatio: 4 / 3,
+    aspectLabel: "4:3",
+    outputWidth: 1200,
+    outputHeight: 900,
+    priority: 90,
+  },
 };
 
 export function getPlatformCoverRequirements(platformIds?: Array<string | null | undefined>): PlatformCoverRequirement[] {