feat: decommission server.sweet.home

Removes all flake artifacts for the retired NFS/ZFS file server:
- flake.nix: drop linode-server, proxmox-server, lxc-server targets
- hosts/server/: delete host identity
- modules/build-types/server.nix: delete build type (ZFS pool + NFS exports)
- vars/per-machine/{linode,lxc,proxmox}-server/: delete clan vars
- secrets/server.keytab: delete IPA keytab
- .sops.yaml: remove server key anchors, strip from common.yaml recipients,
  delete server.yaml and server.keytab creation rules
- variables.nix: remove serverIp, serverStorageIp (nfsServerHost/storageRoot
  retained — pxe-boot/mount-pxe-images.nix still references them)
- docs: mark server decommissioned in ip-addressing.md

Docker NFS mounts already pointed at nfs.storage.home (previous commit).
VM destruction and DNS cleanup (server.sweet.home, server.storage.home
A/PTR records) to follow once the VM is confirmed stopped.

Co-Authored-By: Claude Sonnet 4.6 <noreply@anthropic.com>
Claude-Session: https://claude.ai/code/session_01J8djTWdXVzXZc99iujU6T2

variables.nix

@@ -15,7 +15,6 @@
   nixCacheIp = "192.168.2.224"; # nix-cache LXC container LAN IP
   tailscaleRouterIp = "192.168.2.222"; # tailscale-router LXC container LAN IP
   torRelayIp = "192.168.2.221"; # tor-relay LXC container LAN IP
-  serverIp = "192.168.2.226"; # server (NFS/ZFS) Proxmox VM LAN IP
   dockerIp = "192.168.2.225"; # docker Proxmox VM LAN IP
   pbsIp = "192.168.2.244"; # Proxmox Backup Server LAN IP (not NixOS-managed)
   domainControllerIp = "192.168.2.253"; # FreeIPA domain controller — authoritative DNS for sweet.home (not NixOS-managed)
@@ -124,7 +123,6 @@
   haServerVip = "192.168.20.229"; # storage-client floating VIP on vmbr2 (Pacemaker IPaddr2 vip-storage, VLAN 20)
   haServerLanVip = "192.168.2.229"; # LAN floating VIP on vmbr0 (Pacemaker IPaddr2 vip-lan) — NFS access
   dockerStorageIp = "192.168.20.225"; # docker CT storage-client IP (vmbr2 / eth1, VLAN 20)
-  serverStorageIp = "192.168.20.226"; # server VM storage-client IP (vmbr2 / ens19, VLAN 20) — temporary, for final rsync
   haClientCidr = "192.168.20.0/24"; # storage-client subnet — VLAN 20, internal to pve1 only
   haClientPrefixLength = 24; # storage-client subnet prefix length (/24)
   haStorageRoot = "/srv/ha-data"; # XFS-over-DRBD mount point on the Active node