feat: initial VRRP implementation with health checking

- VRRP protocol implementation (RFC 3768/5798)
- Virtual IP management (add/remove VIPs)
- State machine (INIT/BACKUP/MASTER/FAULT)
- Priority-based master election
- Gratuitous ARP for network updates
- Health checking (TCP, HTTP, ICMP, Script)
- Configuration hot-reload (SIGHUP)

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main.go

@@ -0,0 +1,9 @@
+package main
+
+import (
+	"github.com/loveuer/go-alived/internal/cmd"
+)
+
+func main() {
+	cmd.Execute()
+}