ci: track act_runner config with Docker socket mount

Documents the NAS runner configuration needed for Testcontainers.
Must be deployed to the runner host alongside the act_runner binary.

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

runner-config.yaml

@@ -0,0 +1,12 @@
+# runner-config.yaml — only the relevant section
+container:
+  # passed as DOCKER_HOST inside the job container
+  docker_host: "unix:///var/run/docker.sock"
+  # whitelists the socket path so workflows can mount it
+  valid_volumes:
+    - "/var/run/docker.sock"
+  # appended to `docker run` when the runner spawns a job container
+  options: "-v /var/run/docker.sock:/var/run/docker.sock"
+  # keep network mode default (bridge) — Testcontainers handles its own networking
+  force_pull: false
+