fix(ci): lowercase GHCR owner name and update actions versions

- Fix "repository name must be lowercase" error for GHCR tags
- Update actions/checkout to v5, docker/build-push-action to v6

Co-Authored-By: Claude Opus 4.6 <noreply@anthropic.com>

.github/workflows/docker-publish.yml

@@ -17,7 +17,7 @@ jobs:
 
     steps:
       - name: Checkout repository
-        uses: actions/checkout@v4
+        uses: actions/checkout@v5
         with:
           fetch-depth: 0
 
@@ -41,7 +41,8 @@ jobs:
         run: |
           BRANCH="${GITHUB_REF##*/}"
           DH_IMAGE="${{ secrets.DOCKERHUB_USERNAME }}/${{ env.IMAGE_NAME }}"
-          GH_IMAGE="ghcr.io/${{ github.repository_owner }}/${{ env.IMAGE_NAME }}"
+          OWNER_LC=$(echo "${{ github.repository_owner }}" | tr '[:upper:]' '[:lower:]')
+          GH_IMAGE="ghcr.io/${OWNER_LC}/${{ env.IMAGE_NAME }}"
           TAG="${{ steps.get_tag.outputs.tag }}"
 
           if [ "$BRANCH" = "main" ]; then
@@ -69,7 +70,7 @@ jobs:
           password: ${{ secrets.GITHUB_TOKEN }}
 
       - name: Build and push
-        uses: docker/build-push-action@v5
+        uses: docker/build-push-action@v6
         with:
           context: .
           file: ./Dockerfile