ci: add GHCR publish workflow gated by tests

- build & push image on tag
- publish :latest only for semver tags
- multi-arch (amd64, arm64)

https://chatgpt.com/share/694ae4b0-ca28-800f-863c-0916a2f62a43

.github/workflows/publish-image.yml

@@ -0,0 +1,74 @@
+name: publish-image
+
+on:
+  push:
+    tags:
+      - "*"
+
+jobs:
+  tests:
+    uses: ./.github/workflows/reusable-test.yml
+
+  build-and-push:
+    needs: tests
+    runs-on: ubuntu-latest
+
+    permissions:
+      contents: read
+      packages: write
+
+    steps:
+      - name: Checkout
+        uses: actions/checkout@v4
+
+      - name: Set up QEMU
+        uses: docker/setup-qemu-action@v3
+
+      - name: Set up Docker Buildx
+        uses: docker/setup-buildx-action@v3
+
+      - name: Extract tag
+        id: meta
+        run: |
+          echo "tag=${GITHUB_REF_NAME}" >> "$GITHUB_OUTPUT"
+
+      - name: Check semver tag
+        id: semver
+        run: |
+          if [[ "${GITHUB_REF_NAME}" =~ ^v?[0-9]+\.[0-9]+\.[0-9]+$ ]]; then
+            echo "is_semver=true" >> "$GITHUB_OUTPUT"
+          else
+            echo "is_semver=false" >> "$GITHUB_OUTPUT"
+          fi
+
+      - name: Log in to GHCR
+        uses: docker/login-action@v3
+        with:
+          registry: ghcr.io
+          username: ${{ github.actor }}
+          password: ${{ secrets.GITHUB_TOKEN }}
+
+      - name: Build and push (tag)
+        uses: docker/build-push-action@v6
+        with:
+          context: .
+          file: ./Dockerfile
+          push: true
+          platforms: linux/amd64,linux/arm64
+          tags: |
+            ghcr.io/${{ github.repository }}:${{ steps.meta.outputs.tag }}
+          cache-from: type=gha
+          cache-to: type=gha,mode=max
+
+      - name: Build and push (latest)
+        if: steps.semver.outputs.is_semver == 'true'
+        uses: docker/build-push-action@v6
+        with:
+          context: .
+          file: ./Dockerfile
+          push: true
+          platforms: linux/amd64,linux/arm64
+          tags: |
+            ghcr.io/${{ github.repository }}:latest
+          cache-from: type=gha
+          cache-to: type=gha,mode=max