Fix build_spec for ARM64 cross-build with buildx/QEMU, add IAM docs

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

build_spec.yaml

@@ -1,6 +1,6 @@
 version: 0.1
 component: build
-timeoutInSeconds: 1200
+timeoutInSeconds: 1800
 runAs: root
 shell: bash
 
@@ -13,6 +13,13 @@ env:
     - FRONTEND_IMAGE
 
 steps:
+  - type: Command
+    name: "Setup buildx for ARM64"
+    command: |
+      docker run --rm --privileged multiarch/qemu-user-static --reset -p yes
+      docker buildx create --name armbuilder --use
+      docker buildx inspect --bootstrap
+
   - type: Command
     name: "Set image tag"
     command: |
@@ -27,20 +34,22 @@ steps:
     name: "Build backend image"
     command: |
       cd backend-java
-      docker build --platform linux/arm64 \
+      docker buildx build --platform linux/arm64 \
         -t "${BACKEND_IMAGE}" \
         -t "${REGISTRY}/backend:latest" \
+        --load \
         .
 
   - type: Command
     name: "Build frontend image"
     command: |
       cd frontend
-      docker build --platform linux/arm64 \
+      docker buildx build --platform linux/arm64 \
         --build-arg NEXT_PUBLIC_GOOGLE_MAPS_API_KEY="${NEXT_PUBLIC_GOOGLE_MAPS_API_KEY}" \
         --build-arg NEXT_PUBLIC_GOOGLE_CLIENT_ID="${NEXT_PUBLIC_GOOGLE_CLIENT_ID}" \
         -t "${FRONTEND_IMAGE}" \
         -t "${REGISTRY}/frontend:latest" \
+        --load \
         .
 
 outputArtifacts: