feat(smzdm): require 1:1 cover and surface image fetch failure prompt

Add SMZDM to the cover-required platform list on both client and server,
register a 800x800 native cover spec in the admin cover catalog, and
normalize the desktop-client `smzdm_image_fetch_failed` adapter error to a
user-friendly Chinese prompt across the publisher error pipeline.

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

apps/desktop-client/src/main/adapters/smzdm.ts

@@ -787,7 +787,7 @@ function failureResult(
   if (message.startsWith('smzdm_image_fetch_failed')) {
     return {
       status: 'failed',
-      summary: '什么值得买正文图片读取失败，请检查文章图片后重试。',
+      summary: '图片获取错误，请检查你文章和封面图片是否正确',
       error: {
         code: 'smzdm_image_fetch_failed',
         message,