sysmig: migration runner + initial 4 migrations (swap, daemon trims)

- up/down/status interface, history in /var/lib/sysmig/applied
- 001 swap 2GB + swappiness=10, 002-004 trim unneeded daemons (~56MB)
- google-osconfig-agent intentionally kept
- all messages/comments in ASCII English (console font safety)

migrations/002-disable-networkd-dispatcher.sh

@@ -0,0 +1,11 @@
+#!/usr/bin/env bash
+# 002-disable-networkd-dispatcher - Stop network event hook daemon (~27MB)
+# Unnecessary on a simple server with static network config. Package kept.
+set -euo pipefail
+
+case "${1:-}" in
+  up)   systemctl disable --now networkd-dispatcher.service
+        echo "    networkd-dispatcher stopped and disabled" ;;
+  down) systemctl enable --now networkd-dispatcher.service
+        echo "    networkd-dispatcher re-enabled" ;;
+esac