Install Docker CLI in build job

node:20-bookworm doesn't include the Docker CLI; install docker.io via
apt before the buildx and registry steps.

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

.forgejo/workflows/deploy.yml

@@ -82,6 +82,9 @@ jobs:
             - name: ⬇️ Checkout repo
               uses: https://github.com/actions/checkout@v4
 
+            - name: 🐳 Install Docker CLI
+              run: apt-get update -qq && apt-get install -y -qq docker.io
+
             - name: 🐳 Set up Docker Buildx
               uses: https://github.com/docker/setup-buildx-action@v3