feat(ci): publish Docker image to Docker Hub and GHCR

Add dual-registry publishing to both Docker Hub (rootfr/jmap-webmail)
and GitHub Container Registry. Multi-arch support for amd64/arm64.

.github/workflows/docker-publish.yml

@@ -20,10 +20,6 @@ on:
     tags: ["v*.*.*"]
   workflow_dispatch:
 
-env:
-  REGISTRY: ghcr.io
-  IMAGE_NAME: ${{ github.repository }}
-
 jobs:
   build-and-push:
     runs-on: ubuntu-latest
@@ -41,10 +37,16 @@ jobs:
       - name: Set up Docker Buildx
         uses: docker/setup-buildx-action@v3
 
+      - name: Log in to Docker Hub
+        uses: docker/login-action@v3
+        with:
+          username: ${{ secrets.DOCKERHUB_USERNAME }}
+          password: ${{ secrets.DOCKERHUB_TOKEN }}
+
       - name: Log in to GHCR
         uses: docker/login-action@v3
         with:
-          registry: ${{ env.REGISTRY }}
+          registry: ghcr.io
           username: ${{ github.actor }}
           password: ${{ secrets.GITHUB_TOKEN }}
 
@@ -52,11 +54,14 @@ jobs:
         id: meta
         uses: docker/metadata-action@v5
         with:
-          images: ${{ env.REGISTRY }}/${{ env.IMAGE_NAME }}
+          images: |
+            rootfr/jmap-webmail
+            ghcr.io/${{ github.repository }}
           tags: |
             type=raw,value=latest,enable={{is_default_branch}}
             type=semver,pattern={{version}}
             type=semver,pattern={{major}}.{{minor}}
+            type=sha,prefix=
 
       - name: Build and push
         uses: docker/build-push-action@v6