ci: add GHCR publish workflow (Phase 6)

.github/workflows/publish-ghcr.yml

@@ -0,0 +1,47 @@
+# Auto-generated by J1 pipeline (Phase 6). Publishes multi-service images to ghcr.io.
+name: Publish images to GHCR
+on:
+  push:
+    branches: [main, master]
+    tags: ['v*']
+  workflow_dispatch:
+env:
+  REGISTRY: ghcr.io
+jobs:
+  build-and-push:
+    runs-on: ubuntu-latest
+    permissions:
+      contents: read
+      packages: write
+    strategy:
+      matrix:
+        service:
+          - { name: "backend", context: "backend", dockerfile: "Dockerfile" }
+          - { name: "ffmpeg", context: "ffmpeg", dockerfile: "Dockerfile" }
+          - { name: "frontend", context: "frontend", dockerfile: "Dockerfile" }
+    steps:
+      - uses: actions/checkout@v4
+      - uses: docker/login-action@v3
+        with:
+          registry: ${{ env.REGISTRY }}
+          username: ${{ github.actor }}
+          password: ${{ secrets.GITHUB_TOKEN }}
+      - id: meta
+        uses: docker/metadata-action@v5
+        with:
+          images: ${{ env.REGISTRY }}/${{ github.repository }}-${{ matrix.service.name }}
+          tags: |
+            type=ref,event=branch
+            type=semver,pattern={{version}}
+            type=sha,format=short
+            type=raw,value=latest,enable={{is_default_branch}}
+      - uses: docker/setup-buildx-action@v3
+      - uses: docker/build-push-action@v6
+        with:
+          context: ${{ matrix.service.context }}
+          file: ${{ matrix.service.context }}/${{ matrix.service.dockerfile }}
+          push: true
+          tags: ${{ steps.meta.outputs.tags }}
+          labels: ${{ steps.meta.outputs.labels }}
+          cache-from: type=gha
+          cache-to: type=gha,mode=max