Fix missed renames from act_runner to runner

- registration warning string
- root cobra command Short
- README title and content
- Makefile Go version error message
- Kubernetes example resource names
- s6 service directory

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

scripts/s6/runner/finish

@@ -0,0 +1,3 @@
+#!/usr/bin/env bash
+
+exec s6-svscanctl -t /etc/s6