ci: install docker.io CLI in docker job

The default runner image (catthehacker/ubuntu:act-latest) has the
podman socket mounted at /var/run/docker.sock but no Docker CLI.
Install docker.io to provide the CLI. The socket is accessible as
root, so sudo -E docker build works.

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

.gitea/workflows/ci.yml

@@ -151,23 +151,8 @@ jobs:
     steps:
       - uses: actions/checkout@v4
 
-      - name: Debug docker socket
-        run: |
-          echo "=== User ==="
-          id
-          echo "=== Docker socket ==="
-          ls -la /var/run/docker.sock 2>&1 || echo "not found"
-          echo "=== Tools ==="
-          which docker podman buildah 2>&1 || true
-          echo "=== Docker info (direct) ==="
-          docker info 2>&1 | head -5 || true
-          echo "=== Docker info (sudo) ==="
-          sudo -E docker info 2>&1 | head -5 || true
-          echo "=== Socket stat ==="
-          stat /var/run/docker.sock 2>&1 || echo "stat failed"
-
-      - name: Install skopeo
-        run: sudo apt-get update && sudo apt-get install -y skopeo
+      - name: Install docker CLI and skopeo
+        run: sudo apt-get update && sudo apt-get install -y docker.io skopeo
 
       - name: Build & push mcpd
         run: |