feat: adopt kardianos/service for daemon lifecycle management

Replace manual signal handling in runDaemon() with kardianos/service
for cross-platform service lifecycle (Start/Stop/Run). Add daemon
start/stop/restart subcommands using service.Control(), and improve
status detection with s.Status() plus socket-check fallback.

Custom macOS install logic (dscl, sudoers, pf, plist generation)
is unchanged — only the runtime lifecycle is delegated to the library.

internal/daemon/launchd.go

@@ -546,9 +546,3 @@ func logDebug(debug bool, format string, args ...interface{}) {
 		Logf(format, args...)
 	}
 }
-
-// Logf writes a timestamped message to stderr with the [greywall:daemon] prefix.
-func Logf(format string, args ...interface{}) {
-	ts := time.Now().Format("2006-01-02 15:04:05")
-	fmt.Fprintf(os.Stderr, ts+" [greywall:daemon] "+format+"\n", args...)
-}