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/i18n/messages/en-US.ts

@@ -900,7 +900,7 @@ const enUS = {
       platformsHint: "This stays in sync with Media Management so you can edit the article's publish platforms directly.",
       coverTitle: "Cover image",
       coverHint: "Off by default. Once uploaded, the cover is saved with the article.",
-      coverRequired: "Baijiahao is selected, so the cover image becomes required.",
+      coverRequired: "A selected publishing platform requires a cover image.",
       coverUpload: "Upload cover image",
       coverReplace: "Choose again",
       coverRemove: "Remove cover",
@@ -1060,7 +1060,7 @@ const enUS = {
         partial: "Publish finished with {success} succeeded and {failed} failed.",
         partialTitle: "Partial publish failure",
         selectPlatform: "Choose at least one available platform first.",
-        coverRequired: "Baidu Baijiahao is selected. Please upload a cover image first.",
+        coverRequired: "A selected publishing platform requires a cover image. Please upload one first.",
         failureTitle: "Publish failed",
         failureItem: "Publishing to [{platform}] failed: [{reason}]",
         unknownFailure: "Unknown error",
@@ -1088,10 +1088,10 @@ const enUS = {
     dropzoneTitle: "Upload image",
     dropzoneHint: "Supports PNG, JPG, GIF, and WebP up to 10MB. Uploads are converted to WebP in the browser first.",
     previewTitle: "Cover crop preview",
-    previewHintLocked: "Baijiahao is selected, so the cover will be exported as 16:9 when you confirm.",
+    previewHintLocked: "A selected platform requires a fixed cover ratio, so the cover will be exported using the current platform requirement.",
     previewHintFree: "There is no forced cover ratio right now. You can upload the original image directly or adjust framing before confirming.",
     requirementsTitle: "Platform requirements",
-    requirementsHint: "Requirements switch automatically based on the selected publish platforms. Baijiahao is mandatory.",
+    requirementsHint: "Requirements switch automatically based on the selected publish platforms. Baijiahao and Dongchedi require a cover image.",
     recommendedRatio: "Recommended ratio",
     recommendedSize: "Recommended size",
     required: "Required",