Fix CI/CD: Build amd64 only for PRs to avoid QEMU ARM64 emulation issues

Sharp library native binaries cause QEMU 'Illegal instruction' errors during
ARM64 emulation. This change builds only amd64 for PR checks (faster, reliable)
while maintaining multi-arch (amd64+arm64) builds for main/develop/tags.

.github/workflows/docker-build.yml

@@ -36,10 +36,21 @@ jobs:
     - name: Checkout code
       uses: actions/checkout@v4
 
+    - name: Determine build platforms
+      id: platforms
+      run: |
+        # For PRs, build only amd64 to avoid QEMU emulation issues with Sharp
+        # For main/develop/tags, build multi-arch
+        if [[ "${{ github.event_name }}" == "pull_request" ]]; then
+          echo "platforms=linux/amd64" >> $GITHUB_OUTPUT
+        else
+          echo "platforms=linux/amd64,linux/arm64" >> $GITHUB_OUTPUT
+        fi
+
     - name: Set up Docker Buildx
       uses: docker/setup-buildx-action@v3
       with:
-        platforms: linux/amd64,linux/arm64
+        platforms: ${{ steps.platforms.outputs.platforms }}
 
     - name: Log in to Container Registry
       if: github.event_name != 'pull_request' || github.event.inputs.push == 'true'
@@ -79,7 +90,7 @@ jobs:
         push: ${{ (github.event_name != 'pull_request' || github.event.inputs.push == 'true') && steps.login-ghcr.outcome == 'success' }}
         tags: ${{ steps.meta-backend.outputs.tags }}
         labels: ${{ steps.meta-backend.outputs.labels }}
-        platforms: linux/amd64,linux/arm64
+        platforms: ${{ steps.platforms.outputs.platforms }}
         cache-from: type=gha,scope=backend
         cache-to: type=gha,mode=max,scope=backend
         build-args: |
@@ -116,10 +127,21 @@ jobs:
     - name: Checkout code
       uses: actions/checkout@v4
 
+    - name: Determine build platforms
+      id: platforms
+      run: |
+        # For PRs, build only amd64 to avoid QEMU emulation issues
+        # For main/develop/tags, build multi-arch
+        if [[ "${{ github.event_name }}" == "pull_request" ]]; then
+          echo "platforms=linux/amd64" >> $GITHUB_OUTPUT
+        else
+          echo "platforms=linux/amd64,linux/arm64" >> $GITHUB_OUTPUT
+        fi
+
     - name: Set up Docker Buildx
       uses: docker/setup-buildx-action@v3
       with:
-        platforms: linux/amd64,linux/arm64
+        platforms: ${{ steps.platforms.outputs.platforms }}
 
     - name: Log in to Container Registry
       if: github.event_name != 'pull_request' || github.event.inputs.push == 'true'
@@ -159,7 +181,7 @@ jobs:
         push: ${{ (github.event_name != 'pull_request' || github.event.inputs.push == 'true') && steps.login-ghcr.outcome == 'success' }}
         tags: ${{ steps.meta-frontend.outputs.tags }}
         labels: ${{ steps.meta-frontend.outputs.labels }}
-        platforms: linux/amd64,linux/arm64
+        platforms: ${{ steps.platforms.outputs.platforms }}
         cache-from: type=gha,scope=frontend
         cache-to: type=gha,mode=max,scope=frontend
         build-args: |