Fix Next.js standalone build for Amplify WEB_COMPUTE

- Set output to standalone in next.config.js
- Update build artifacts to use .next/standalone
- Copy static files to standalone directory
- Remove invalid serverActions config

amplify.yml

@@ -10,14 +10,12 @@ frontend:
     build:
       commands:
         - npm run build
+        - cp -r public .next/standalone/
+        - cp -r .next/static .next/standalone/.next/
   artifacts:
-    baseDirectory: ./
+    baseDirectory: .next/standalone
     files:
-      - .next/**/*
-      - node_modules/**/*
-      - package.json
-      - next.config.js
-      - public/**/*
+      - '**/*'
   cache:
     paths:
       - node_modules/**/*