dns: auto-generate zone entries from host configurations

Replace static zone file with dynamically generated records:
- Add homelab.dns module with enable/cnames options
- Extract IPs from systemd.network configs (filters VPN interfaces)
- Use git commit timestamp as zone serial number
- Move external hosts to separate external-hosts.nix

Co-Authored-By: Claude Opus 4.5 <noreply@anthropic.com>

hosts/auth01/configuration.nix

@@ -11,6 +11,8 @@
     ../../common/vm
   ];
 
+  homelab.dns.cnames = [ "ldap" ];
+
   nixpkgs.config.allowUnfree = true;
   # Use the systemd-boot EFI boot loader.
   boot.loader.grub = {

hosts/http-proxy/configuration.nix

@@ -11,6 +11,22 @@
     ../../common/vm
   ];
 
+  homelab.dns.cnames = [
+    "nzbget"
+    "radarr"
+    "sonarr"
+    "ha"
+    "z2m"
+    "grafana"
+    "prometheus"
+    "alertmanager"
+    "jelly"
+    "auth"
+    "lldap"
+    "pyroscope"
+    "pushgw"
+  ];
+
   nixpkgs.config.allowUnfree = true;
   # Use the systemd-boot EFI boot loader.
   boot.loader.grub = {

hosts/nix-cache01/configuration.nix

@@ -11,6 +11,8 @@
     ../../common/vm
   ];
 
+  homelab.dns.cnames = [ "nix-cache" "actions1" ];
+
   fileSystems."/nix" = {
     device = "/dev/disk/by-label/nixcache";
     fsType = "xfs";

hosts/template/configuration.nix

@@ -8,6 +8,9 @@
       ../../system
     ];
 
+  # Template host - exclude from DNS zone generation
+  homelab.dns.enable = false;
+
 
   boot.loader.grub.enable = true;
   boot.loader.grub.device = "/dev/sda";

hosts/testvm01/configuration.nix

@@ -13,6 +13,9 @@
     ../../common/vm
   ];
 
+  # Test VM - exclude from DNS zone generation
+  homelab.dns.enable = false;
+
   nixpkgs.config.allowUnfree = true;
   boot.loader.grub.enable = true;
   boot.loader.grub.device = "/dev/vda";

hosts/vault01/configuration.nix

@@ -14,6 +14,8 @@
     ../../services/vault
   ];
 
+  homelab.dns.cnames = [ "vault" ];
+
   nixpkgs.config.allowUnfree = true;
   boot.loader.grub.enable = true;
   boot.loader.grub.device = "/dev/vda";