fix: remove unnecessary publish-manifest job from Docker workflow

The publish-manifest job was failing because it tried to create manifests
from non-existent architecture-specific tags (latest-amd64, latest-arm64).

docker/build-push-action@v5 already creates multi-arch manifests automatically
when building for multiple platforms, making this job redundant.

The workflow now correctly builds and pushes multi-arch images in a single
step with proper manifest lists included.

🤖 Generated with [Claude Code](https://claude.ai/code)

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

.github/workflows/docker-build.yml

@@ -179,37 +179,9 @@ jobs:
         sarif_file: 'trivy-frontend.sarif'
         category: 'frontend-vulnerabilities'
 
-  publish-manifest:
-    needs: [build-backend, build-frontend]
-    if: github.event_name == 'release' || (github.event_name == 'push' && github.ref == 'refs/heads/main')
-    runs-on: ubuntu-latest
-    permissions:
-      contents: read
-      packages: write
-    
-    steps:
-    - name: Log in to Container Registry
-      uses: docker/login-action@v3
-      with:
-        registry: ${{ env.REGISTRY }}
-        username: ${{ github.actor }}
-        password: ${{ secrets.GITHUB_TOKEN }}
-
-    - name: Create and push multi-arch manifest for Backend
-      run: |
-        docker manifest create \
-          ${{ env.REGISTRY }}/${{ env.BACKEND_IMAGE_NAME }}:latest \
-          --amend ${{ env.REGISTRY }}/${{ env.BACKEND_IMAGE_NAME }}:latest-amd64 \
-          --amend ${{ env.REGISTRY }}/${{ env.BACKEND_IMAGE_NAME }}:latest-arm64
-        docker manifest push ${{ env.REGISTRY }}/${{ env.BACKEND_IMAGE_NAME }}:latest
-
-    - name: Create and push multi-arch manifest for Frontend
-      run: |
-        docker manifest create \
-          ${{ env.REGISTRY }}/${{ env.FRONTEND_IMAGE_NAME }}:latest \
-          --amend ${{ env.REGISTRY }}/${{ env.FRONTEND_IMAGE_NAME }}:latest-amd64 \
-          --amend ${{ env.REGISTRY }}/${{ env.FRONTEND_IMAGE_NAME }}:latest-arm64
-        docker manifest push ${{ env.REGISTRY }}/${{ env.FRONTEND_IMAGE_NAME }}:latest
+  # Note: The publish-manifest job is not needed since docker/build-push-action@v5
+  # automatically creates multi-arch manifests when building for multiple platforms.
+  # The images are already properly tagged and include all architectures.
 
   summary:
     needs: [build-backend, build-frontend]