fix: install Docker CLI in build-and-push job

The Harbor login was failing with:
  Unable to locate executable file: docker

Gitea Actions runners have the Docker socket mounted at
/var/run/docker.sock, but the Docker CLI binary isn't installed in
the default ubuntu-latest container.

Solution:
- Download Docker CLI static binary from Docker's official repository
- Extract to /tmp/docker-cli
- Add to PATH for subsequent steps
- This allows docker/login-action and docker/build-push-action to work

Co-Authored-By: Claude Sonnet 4.5 <noreply@anthropic.com>

.gitea/workflows/main.yml

@@ -297,6 +297,14 @@ jobs:
       - name: Checkout code
         uses: actions/checkout@v4
 
+      - name: Install Docker CLI
+        run: |
+          mkdir -p /tmp/docker-cli
+          curl -fsSL "https://download.docker.com/linux/static/stable/x86_64/docker-24.0.7.tgz" | tar -xz -C /tmp/docker-cli --strip-components=1
+          export PATH="/tmp/docker-cli:$PATH"
+          echo "/tmp/docker-cli" >> $GITHUB_PATH
+          docker --version
+
       - name: Set up Docker Buildx
         uses: docker/setup-buildx-action@v3