Update buildspec to build React app and serve from react-app/dist

Co-Authored-By: Claude Sonnet 4.6 <noreply@anthropic.com>

Author: johnebgood

buildspec.yml

@@ -1,5 +1,17 @@
 version: 0.2
+
+phases:
+  install:
+    runtime-versions:
+      nodejs: 20
+    commands:
+      - cd react-app
+      - npm ci
+  build:
+    commands:
+      - npm run build
+
 artifacts:
   files:
     - '**/*'
-  base-directory: 'webfront'
+  base-directory: 'react-app/dist'