feat(playground): switch to convex-native better-auth

Author: onmax

playground/app/auth.config.ts

@@ -1,3 +1,7 @@
 import { defineClientAuth } from '@onmax/nuxt-better-auth/config'
+import { convexClient, crossDomainClient } from '@convex-dev/better-auth/client/plugins'
 
-export default defineClientAuth({})
+export default defineClientAuth(() => ({
+  baseURL: `${import.meta.env.VITE_CONVEX_SITE_URL}/api/auth`,
+  plugins: [convexClient(), crossDomainClient()],
+}))