Add CI/CD workflow: publish Docker images to GHCR on push to main-bc

.github/workflows/docker-publish-main-bc.yml

@@ -0,0 +1,73 @@
+name: Publish Docker images (main-bc)
+
+# Builds and pushes the frontend (apps/OpenSign) and backend (apps/OpenSignServer)
+# Docker images to GitHub Container Registry whenever main-bc is updated.
+# DigitalOcean App Platform is configured to redeploy automatically when a new
+# image tag is pushed (see deployment docs for the App Spec changes required).
+
+on:
+  push:
+    branches:
+      - main-bc
+
+permissions:
+  contents: read
+  packages: write
+
+env:
+  REGISTRY: ghcr.io
+  IMAGE_OWNER: bycoderstec
+
+jobs:
+  docker:
+    runs-on: ubuntu-latest
+    strategy:
+      matrix:
+        include:
+          - name: opensign
+            dockerfile: apps/OpenSign/Dockerhubfile
+          - name: opensignserver
+            dockerfile: apps/OpenSignServer/Dockerhubfile
+
+    steps:
+      - name: Checkout
+        uses: actions/checkout@v4
+
+      # Enable emulation so we can build for arm64 on amd64 runners
+      - name: Set up QEMU
+        uses: docker/setup-qemu-action@v3
+        with:
+          platforms: linux/amd64,linux/arm64
+
+      # Enable Buildx for multi-arch builds and cache support
+      - name: Set up Docker Buildx
+        uses: docker/setup-buildx-action@v3
+
+      - name: Log in to GitHub Container Registry
+        uses: docker/login-action@v3
+        with:
+          registry: ${{ env.REGISTRY }}
+          username: ${{ github.actor }}
+          password: ${{ secrets.GITHUB_TOKEN }}
+
+      - name: Extract metadata (tags, labels) for Docker
+        id: meta
+        uses: docker/metadata-action@v5
+        with:
+          images: ${{ env.REGISTRY }}/${{ env.IMAGE_OWNER }}/${{ matrix.name }}
+          tags: |
+            type=raw,value=main-bc
+            type=raw,value=latest
+            type=sha,prefix=,format=short
+
+      - name: Build and push (multi-arch)
+        uses: docker/build-push-action@v6
+        with:
+          context: .
+          file: ${{ matrix.dockerfile }}
+          push: true
+          platforms: linux/amd64,linux/arm64
+          tags: ${{ steps.meta.outputs.tags }}
+          labels: ${{ steps.meta.outputs.labels }}
+          cache-from: type=gha,scope=${{ matrix.name }}
+          cache-to: type=gha,mode=max,scope=${{ matrix.name }}