fix: Install Node.js in Gitea act runner container for GitHub Actions support

- Add Node.js installation in runner startup command
- Use :host labels instead of docker paths (as recommended)
- Add auto-registration check to handle emptyDir volume resets
- Fix working directory to /data for .runner file location

This fixes the 'Cannot find: node in PATH' error when running
GitHub Actions like actions/checkout@v4 and actions/setup-node@v4

k8s/gitea-runners/deployment.yaml

@@ -31,6 +31,13 @@ spec:
           readOnly: true
       - name: runner
         image: gitea/act_runner:latest
+        command:
+        - sh
+        - -c
+        - |
+          apk add --no-cache nodejs npm || true
+          cd /data
+          exec /usr/local/bin/act_runner daemon
         env:
         - name: GITEA_INSTANCE_URL
           value: "http://gitea.gitea.svc.cluster.local:3000"