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.

contrib/monitor-lets-go-suspend.service

@@ -0,0 +1,20 @@
+[Unit]
+Description=monitor-lets-go -- restore portable layout before suspend
+Documentation=https://github.com/mat/monitor-lets-go
+
+# Run before the system enters sleep. The ExecStop action writes a portable
+# monitor config so that on resume the compositor never loads a stale docked
+# config that would leave the built-in display disabled.
+Before=sleep.target
+
+[Service]
+# RemainAfterExit: ExecStop runs when the service is stopped (before sleep).
+# This is the standard pattern for systemd suspend hooks.
+Type=oneshot
+RemainAfterExit=yes
+
+ExecStart=/bin/true
+ExecStop=%h/.local/bin/monitor-lets-go -config %h/.config/monitor-lets-go/config.yaml -apply portable -no-reload
+
+[Install]
+WantedBy=sleep.target