Add core modules (SSH args parser, cache, resolver, NetBox client) with tests

internal/ssh/exec.go

@@ -0,0 +1,19 @@
+package ssh
+
+import (
+	"fmt"
+	"os"
+	"os/exec"
+	"syscall"
+)
+
+// Exec replaces the current process with the native ssh client via syscall.Exec.
+// All existing SSH configs, keys, and agent forwarding remain intact.
+func Exec(args []string) error {
+	sshPath, err := exec.LookPath("ssh")
+	if err != nil {
+		return fmt.Errorf("ssh not found in PATH: %w", err)
+	}
+	argv := append([]string{"ssh"}, args...)
+	return syscall.Exec(sshPath, argv, os.Environ())
+}