feat: adguard-register — auto DNS registration agent for AdGuard Home

Registers {hostname}.home.dustin.coffee → host IP on boot via AdGuard Home API.
Deploy to any LXC/VM with ./install.sh — supports root (system service),
sudo user (system via sudo), and unprivileged user (systemd --user or crontab).

Files:
- adguard-register.sh — detects hostname+IP, idempotent create/update
- install.sh — deployment script with auto-detection of install method
- uninstall.sh — removes service and binary
- README.md — full documentation

Tested across 24 hosts (LXCs and VMs) on a 172.20.0.0/16 home lab network.

.gitignore

@@ -0,0 +1,3 @@
+*.swp
+*~
+.DS_Store