docs(network): establish IP addressing scheme and update infra IPs

Defines the new structured 192.168.2.0/24 layout:
- .10–.59   client DHCP (router-assigned, DNS → .253)
- .220–.229 virtual nodes (VMs / LXC containers)
- .230–.239 expansion buffer
- .240–.249 physical nodes (pve1 at .245, PBS at .244)
- .250–.253 network services (router .254, FreeIPA/DC .253)

Storage network 192.168.4.0/29 defined for HA DRBD replication
(internal vmbr1 bridge, no uplink). Host octet matches LAN throughout.

Updates variables.nix: pxeServerIp .247→.223, pbsIp .108→.244,
adds domainControllerIp .253. Updates pxe-boot.md IP references.
Full migration before/after table in docs/ip-addressing.md.

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

docs/pxe-boot.md

@@ -64,8 +64,8 @@ The HTTP iPXE chain is:
 ```text
 undionly.kpxe or ipxe.efi
   -> autoexec.ipxe from the TFTP root, when iPXE requests it
-  -> http://192.168.2.247/boot.ipxe
-  -> http://192.168.2.247/menu.ipxe
+  -> http://192.168.2.223/boot.ipxe
+  -> http://192.168.2.223/menu.ipxe
 ```
 
 The generated menu currently exposes entries for:
@@ -141,7 +141,7 @@ The `stage-systemrescue.service` oneshot extracts that ISO into:
 /srv/pxe/http/systemrescue
 ```
 
-The rescue menu entry then chains `http://192.168.2.247/systemrescue.ipxe`,
+The rescue menu entry then chains `http://192.168.2.223/systemrescue.ipxe`,
 which loads the SystemRescue kernel and initramfs from the extracted tree and
 uses `archiso_http_srv` to fetch the squashfs payload over HTTP.