fix(share): register share schema in global registry

The share schema was imported but never added to globalSchemas, so
getSchema('global', 'share') returned null and the page fell back to
route meta with empty groups, rendering "暂无配置项".

assets/admin/src/schema/sections/global/index.js

@@ -28,4 +28,5 @@ export const globalSchemas = {
   seo: seoSchema,
   'code-highlight': codeHighlightSchema,
   'system-notice': systemNoticeSchema,
+  share: shareSchema,
 }