feat(publish): require cover image for WeChat Official Account

WeChat 公众号在管理员/运营者授权发布场景下需要 2.35:1 封面，
新增共享 publishPlatformRequiresCover 校验并同步前端封面要求与文案，
避免在调度与即时发布两条路径上重复维护平台名单。

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

apps/admin-web/src/i18n/messages/en-US.ts

@@ -1101,7 +1101,7 @@ const enUS = {
     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 and Dongchedi require a cover image.",
+    requirementsHint: "Requirements switch automatically based on the selected publish platforms. WeChat Official Account, Baijiahao, and Dongchedi require a cover image.",
     recommendedRatio: "Recommended ratio",
     recommendedSize: "Recommended size",
     required: "Required",

apps/admin-web/src/i18n/messages/zh-CN.ts

@@ -1110,7 +1110,7 @@ const zhCN = {
     previewHintLocked: "已选择需要固定封面比例的平台，确认时会按当前平台要求输出封面。",
     previewHintFree: "当前不限制封面比例，可直接上传原图；如需调整也可拖拽缩放后再确认。",
     requirementsTitle: "平台封面要求",
-    requirementsHint: "会根据当前选中的发布平台自动切换要求，百家号和懂车帝为强制上传。",
+    requirementsHint: "会根据当前选中的发布平台自动切换要求，微信公众号、百家号和懂车帝为强制上传。",
     recommendedRatio: "推荐比例",
     recommendedSize: "推荐尺寸",
     required: "必传",

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

@@ -24,6 +24,15 @@ const defaultRequirement = {
 };
 
 const requirementCatalog: Record<string, Partial<PlatformCoverRequirement>> = {
+  weixin_gzh: {
+    required: true,
+    supportMode: "native",
+    aspectRatio: 2.35,
+    aspectLabel: "2.35:1",
+    outputWidth: 1200,
+    outputHeight: 511,
+    priority: 110,
+  },
   baijiahao: {
     required: true,
     supportMode: "native",