feat(pxe-boot): enroll in FreeIPA domain

- Add IPA client module with pre-provisioned keytab
- Set networking.domain for correct Kerberos FQDN
- Encrypted keytab covers lxc-pxe-boot and proxmox-pxe-boot age keys

Co-Authored-By: Claude Sonnet 4.6 <noreply@anthropic.com>

hosts/pxe-boot/host.nix

@@ -1,8 +1,16 @@
 { vars, ... }:
 
 {
+  imports = [
+    (import ../../modules/ipa/client.nix {
+      keytabSopsFile = ../../secrets/pxe-boot.keytab;
+      caCertFile     = ../../certs/ipa-ca.crt;
+    })
+  ];
+
   networking = {
     hostName = "pxe-boot";
+    domain   = vars.homeDomain;
     useDHCP = false;
     interfaces.${vars.lxcLanInterface}.ipv4.addresses = [{
       address = vars.pxeServerIp;