Update CI/CD to push Docker images to GitHub Container Registry

- Replace Docker Hub with GitHub Container Registry (ghcr.io)
- Use GitHub token authentication instead of separate Docker credentials
- Add packages:write permission for GHCR access
- Images will now be available at ghcr.io/rossigee/bucketsyncd

Author: rossigee

.github/workflows/ci.yml

@@ -12,6 +12,7 @@ permissions:
   contents: write
   security-events: write
   actions: read
+  packages: write
 
 env:
   GO_VERSION: '1.25.0'
@@ -203,19 +204,19 @@ jobs:
     - name: Set up Docker Buildx
       uses: docker/setup-buildx-action@v3
 
-    - name: Log in to Docker Hub
+    - name: Log in to GitHub Container Registry
       if: github.event_name == 'release'
       uses: docker/login-action@v3
-      continue-on-error: true
       with:
-        username: ${{ secrets.DOCKER_USERNAME }}
-        password: ${{ secrets.DOCKER_PASSWORD }}
+        registry: ghcr.io
+        username: ${{ github.actor }}
+        password: ${{ secrets.GITHUB_TOKEN }}
 
     - name: Extract metadata
       id: meta
       uses: docker/metadata-action@v5
       with:
-        images: ${{ github.repository }}
+        images: ghcr.io/${{ github.repository }}
         tags: |
           type=ref,event=branch
           type=ref,event=pr