Install Docker CLI in build workflow for Debian environment

.gitea/workflows/build.yaml

@@ -23,6 +23,23 @@ jobs:
     steps:
       - uses: actions/checkout@v4
 
+      # node:24-trixie (Debian 13) has git and node but no Docker CLI. Install
+      # the CLI and buildx from Docker's apt repo; the daemon is the runner's.
+      - name: Install Docker CLI
+        run: |
+          install -m 0755 -d /etc/apt/keyrings
+          curl -fsSL https://download.docker.com/linux/debian/gpg -o /etc/apt/keyrings/docker.asc
+          chmod a+r /etc/apt/keyrings/docker.asc
+          cat > /etc/apt/sources.list.d/docker.sources <<SRC
+          Types: deb
+          URIs: https://download.docker.com/linux/debian
+          Suites: $(. /etc/os-release && echo "$VERSION_CODENAME")
+          Components: stable
+          Signed-By: /etc/apt/keyrings/docker.asc
+          SRC
+          apt-get update
+          apt-get install -y --no-install-recommends docker-ce-cli docker-buildx-plugin
+
       - name: Log in to registry
         run: |
           REGISTRY="${SERVER_URL#https://}"