fix(nuxt): transpile app.config files in nitro build (#27342)

packages/nuxt/src/core/nitro.ts

@@ -161,6 +161,8 @@ export async function initNitro (nuxt: Nuxt & { _nitro?: Nitro }) {
         'nuxt3/dist',
         'nuxt-nightly/dist',
         distDir,
+        // Ensure app config files have auto-imports injected even if they are pure .js files
+        ...nuxt.options._layers.map(layer => resolve(layer.config.srcDir, 'app.config')),
       ],
       traceInclude: [
         // force include files used in generated code from the runtime-compiler

test/fixtures/basic/app.config.js

@@ -1,3 +1,4 @@
+// eslint-disable-next-line no-undef
 export default defineAppConfig({
   userConfig: 123,
   nested: {