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/errors.ts

@@ -50,7 +50,7 @@ const errorMessageMap: Record<string, string> = {
   question_limit_reached: "当前关键词下的问题数量已达上限",
   brand_not_found: "品牌不存在或已删除",
   keyword_not_found: "关键词不存在或已删除",
-  publish_cover_required: "已选择百家号，请先上传封面图",
+  publish_cover_required: "当前选择的平台要求上传封面图，请先上传封面图",
   desktop_account_client_missing: "所选账号还没有绑定桌面客户端，暂时无法发布",
   desktop_account_not_found: "所选桌面账号不存在，请刷新后重试",
   desktop_client_offline: "当前登录账号的桌面客户端未在线，请先打开 desktop-client",