feat: restore portable layout on shutdown and before suspend

Add WriteConfig/Prepare backend methods (real for Hyprland, no-op for
Sway), -apply/-prepare/-no-reload CLI flags, ExecStartPre cleanup and
suspend systemd hooks so a stale docked config can never leave the
built-in display disabled after resume.

internal/backend/sway.go

@@ -554,4 +554,16 @@ func (s *swayBackend) Close() error {
 	return nil
 }
 
+// ---------------------------------------------------------------------------
+// WriteConfig / Prepare (no-ops for Sway — no persistent config file)
+// ---------------------------------------------------------------------------
+
+func (s *swayBackend) WriteConfig(ctx context.Context, monitors []MonitorConfig) error {
+	return nil
+}
+
+func (s *swayBackend) Prepare(ctx context.Context) error {
+	return nil
+}
+