fix(schema): evaluate env variables when resolving values

packages/schema/src/config/_app.ts

@@ -51,10 +51,14 @@ export default defineUntypedSchema({
      * NUXT_APP_BASE_URL=/prefix/ node .output/server/index.mjs
      * ```
      */
-    baseURL: process.env.NUXT_APP_BASE_URL || '/',
+    baseURL: {
+      $resolve: async (val) => val || process.env.NUXT_APP_BASE_URL || '/',
+    },
 
     /** The folder name for the built site assets, relative to `baseURL` (or `cdnURL` if set). This is set at build time and should not be customized at runtime. */
-    buildAssetsDir: process.env.NUXT_APP_BUILD_ASSETS_DIR || '/_nuxt/',
+    buildAssetsDir: {
+      $resolve: async (val) => val || process.env.NUXT_APP_BUILD_ASSETS_DIR || '/_nuxt/',
+    },
 
     /**
      * The folder name for the built site assets, relative to `baseURL` (or `cdnURL` if set).