Fix SAM build: use npm run build to get esbuild on PATH

Author: smessmer

.github/workflows/backend.yml

@@ -34,12 +34,23 @@ jobs:
         run: npm test
       - name: Build
         working-directory: backend
-        run: npm run build
+        run: |
+          echo "=== Before build ==="
+          ls -la
+          echo "=== Running npm run build (uses node_modules/.bin for esbuild) ==="
+          npm run build
+          echo "=== After build ==="
+          ls -la
+          ls -la .aws-sam/ || echo "ERROR: .aws-sam not created by build!"
+          ls -la .aws-sam/build/ || echo "ERROR: .aws-sam/build not found!"
+          echo "=== PWD ==="
+          pwd
       - name: Store artifacts
         uses: actions/upload-artifact@v4
         with:
           name: sam-build
           path: backend/.aws-sam
+          if-no-files-found: error
 
   deploy:
     needs: build