refactor(admin): clean up audit/permission/paid content config

- P1: remove the duplicate "审核联动" (ai_moderate_background/submit)
  block from the attachment permissions page; those settings live in
  the "评论审核" / API content audit surfaces.
- P2: rename the "内容审核" submenu to "评论审核" (permissions domain).
- P4: remove the "下载/付费内容中心" page and its schema/route chain;
  hardcode runtime policy so download always supports credit purchase
  and paid content is limited to posts. Drop the now-dead
  cms_features.download_credit flag and parse_slug_list helper.

assets/admin/src/constants/sections/index.js

@@ -15,7 +15,7 @@ const SECTION_DEFAULT_CHILDREN = {
   'post-list': 'post-list-page',
   permissions: 'permissions-comment',
   users: 'users-auth',
-  payment: 'payment-paid',
+  payment: 'payment-recharge',
   extensions: 'extensions-ip',
   tools: 'tools-import-export',
   'theme-info': 'theme-info-dashboard',