feat(client): declare $frontmatter and $params as ComponentCustomProperties

Allows the template globals to resolve and be typed in editors.

Co-Authored-By: Claude Fable 5 <noreply@anthropic.com>

src/client/index.ts

@@ -9,6 +9,7 @@ export type { Route, VitePressData } from './shared'
 export type { EnhanceAppContext, Theme } from './app/theme'
 
 // shared types
+import type { PageData } from '../../types/shared'
 export type { HeadConfig, Header, PageData, SiteData } from '../../types/shared'
 
 // components
@@ -36,4 +37,9 @@ declare module 'vue' {
     ClientOnly: typeof ClientOnly
     Content: typeof Content
   }
+
+  interface ComponentCustomProperties {
+    $frontmatter: PageData['frontmatter']
+    $params: PageData['params']
+  }
 }