Run build job in docker:27-cli container with host socket mount

act_runner spawns an ephemeral container per job; the default image
lacks the docker CLI and cannot reach the host's Docker daemon. Use
the official docker:27-cli image and bind-mount /var/run/docker.sock
so docker build/push target the host engine.

Requires runner config.yaml to include /var/run/docker.sock in
container.valid_volumes; otherwise the mount is rejected.

Co-Authored-By: Claude Opus 4.7 (1M context) <noreply@anthropic.com>

.gitea/workflows/flow.yml

@@ -30,6 +30,10 @@ jobs:
   # ============================================================
   build:
     runs-on: ubuntu-latest
+    container:
+      image: docker:27-cli
+      volumes:
+        - /var/run/docker.sock:/var/run/docker.sock
     outputs:
       image_tag: ${{ steps.meta.outputs.tag }}
     steps: