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>

internal/app/cmd/cmd.go

@@ -18,7 +18,7 @@ func Execute(ctx context.Context) {
 	// ./runner
 	rootCmd := &cobra.Command{
 		Use:          "runner [event name to run]\nIf no event name passed, will default to \"on: push\"",
-		Short:        "Run GitHub actions locally by specifying the event name (e.g. `push`) or an action name directly.",
+		Short:        "Actions runner for Gitea.",
 		Args:         cobra.MaximumNArgs(1),
 		Version:      ver.Version(),
 		SilenceUsage: true,