fix(workflow): remove docker-buildx-action for compatibility

Remove docker/setup-buildx-action step which requires special
Docker daemon configuration. Use plain docker build commands
instead for better compatibility with Gitea Actions runner.

This simplifies the workflow and works with the standard
catthehacker/ubuntu:act-latest images that have Docker CLI
pre-installed.

🤖 Generated with [Claude Code](https://claude.com/claude-code)

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

.gitea/workflows/build.yaml

@@ -15,9 +15,6 @@ jobs:
       - name: Checkout code
         uses: actions/checkout@v4
 
-      - name: Set up Docker Buildx
-        uses: docker/setup-buildx-action@v3
-
       - name: Determine image tags
         id: tags
         run: |