ci(docker): Removes Docker Hub login and image push configuration

The Docker Hub login step and image push configuration have been removed from the GitHub Actions workflow,

retaining only the push logic for the GitHub Container Registry. This simplifies the CI process and avoids

unnecessary Docker Hub-related operations.

.github/workflows/docker.yml

@@ -48,13 +48,6 @@ jobs:
           username: ${{ github.actor }}
           password: ${{ secrets.GITHUB_TOKEN }}
 
-      - name: Log in to Docker Hub
-        uses: docker/login-action@v3
-        with:
-          username: ${{ secrets.DOCKERHUB_USERNAME }}
-          password: ${{ secrets.DOCKERHUB_TOKEN }}
-        continue-on-error: true
-
       # Resolve VERSION:
       # - release event: use release tag_name (e.g., v0.3.0)
       # - workflow_dispatch: use input version (default: latest)
@@ -137,7 +130,6 @@ jobs:
         with:
           images: |
             ${{ env.REGISTRY }}/${{ env.IMAGE_NAME }}
-            ${{ secrets.DOCKERHUB_USERNAME && format('docker.io/{0}/drip-server', secrets.DOCKERHUB_USERNAME) || '' }}
           tags: |
             # Main tag, e.g. v0.3.0 or latest
             type=raw,value=${{ steps.version.outputs.VERSION }}