fix(inertia): make useAppConfig reactive

Follow-up 869c0708bd

src/runtime/inertia/stubs.ts

@@ -9,6 +9,7 @@ import { usePage } from '@inertiajs/vue3'
 
 export { useHead } from '@unhead/vue'
 
+export { useAppConfig } from '../vue/composables/useAppConfig'
 export { defineShortcuts } from '../composables/defineShortcuts'
 export { defineLocale } from '../composables/defineLocale'
 export { useLocale } from '../composables/useLocale'
@@ -41,8 +42,6 @@ export const useColorMode = () => {
   }
 }
 
-export const useAppConfig = () => appConfig
-
 export const useCookie = <T = string>(
   _name: string,
   _options: Record<string, any> = {}