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>

services/ns/external-hosts.nix

@@ -0,0 +1,52 @@
+# DNS records for hosts not managed by this flake
+# These are manually maintained and combined with auto-generated records
+{
+  aRecords = {
+    # 8_k8s
+    "kube-blue1" = "10.69.8.150";
+    "kube-blue2" = "10.69.8.151";
+    "kube-blue3" = "10.69.8.152";
+    "kube-blue4" = "10.69.8.153";
+    "kube-blue5" = "10.69.8.154";
+    "kube-blue6" = "10.69.8.155";
+    "kube-blue7" = "10.69.8.156";
+    "kube-blue8" = "10.69.8.157";
+    "kube-blue9" = "10.69.8.158";
+    "kube-blue10" = "10.69.8.159";
+
+    # 10
+    "gw" = "10.69.10.1";
+
+    # 12_CORE
+    "virt-mini1" = "10.69.12.11";
+    "nas" = "10.69.12.50";
+    "nzbget-jail" = "10.69.12.51";
+    "restic" = "10.69.12.52";
+    "radarr-jail" = "10.69.12.53";
+    "sonarr-jail" = "10.69.12.54";
+    "bazarr" = "10.69.12.55";
+    "mpnzb" = "10.69.12.57";
+    "pve1" = "10.69.12.75";
+    "inc1" = "10.69.12.80";
+    "inc2" = "10.69.12.81";
+
+    # 22_WLAN
+    "unifi-ctrl" = "10.69.22.5";
+
+    # 30
+    "gunter" = "10.69.30.105";
+
+    # 31
+    "media" = "10.69.31.50";
+
+    # 99_MGMT
+    "sw1" = "10.69.99.2";
+    "testing" = "10.69.33.33";
+  };
+
+  cnames = {
+    # k8s services
+    "rook" = "kube-blue4";
+    "git" = "kube-blue5";
+  };
+}