feat(ha): add vmbr2 storage-client network and corosync ring1

Infrastructure changes already applied to pve1:
- vmbr2 internal bridge created (192.168.5.0/24, no physical uplink)
- VM 200 (ha-server-1): net2 added → vmbr2 (ens20)
- VM 201 (ha-server-2): net2 added → vmbr2 (ens20)
- CT 105 (docker): net1 added → vmbr2 (eth1)
- VM 101 (server): net1 added → vmbr2 (ens19) — needs reboot to activate

NixOS config (deploy to ha nodes to complete; docker/server at cutover):
- ha-server-{1,2}/host.nix: ens20 with 192.168.5.{228,227}/24
- docker/host.nix: eth1 with 192.168.5.225/24
- server/host.nix: ens19 with 192.168.5.226/24
- cluster-config.nix: corosync ring1 on LAN IPs as backup heartbeat path
- cluster-config.nix: allow haClientCidr (192.168.5.0/24) in iptables
- ha-server.nix: NFS exports now allow both lanCidr and haClientCidr
- VIP moves from 192.168.2.229 (vmbr0/LAN) to 192.168.5.229 (vmbr2)
- iSCSI portal to be rebound from [::0] to 192.168.5.229 at cutover

variables.nix: haStorageCidr corrected to 192.168.4.224/29; new vars:
vmStorageClientInterface, lxcStorageInterface, haServer{1,2}ClientIp,
dockerStorageIp, serverStorageIp, haClientCidr/PrefixLength; haServerVip
updated to 192.168.5.229.

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

hosts/ha-server-1/host.nix

@@ -4,14 +4,11 @@
     hostName = vars.haServer1Host;
     hostId = "3a4b5c6d";
     useDHCP = false;
-    interfaces.${vars.vmLanInterface}.ipv4.addresses = [{
-      address = vars.haServer1Ip;
-      prefixLength = vars.lanPrefixLength;
-    }];
-    interfaces.${vars.vmStorageInterface}.ipv4.addresses = [{
-      address = vars.haServer1StorageIp;
-      prefixLength = vars.haStoragePrefixLength;
-    }];
+    interfaces = {
+      ${vars.vmLanInterface}.ipv4.addresses = [{ address = vars.haServer1Ip; prefixLength = vars.lanPrefixLength; }];
+      ${vars.vmStorageInterface}.ipv4.addresses = [{ address = vars.haServer1StorageIp; prefixLength = vars.haStoragePrefixLength; }];
+      ${vars.vmStorageClientInterface}.ipv4.addresses = [{ address = vars.haServer1ClientIp; prefixLength = vars.haClientPrefixLength; }];
+    };
     defaultGateway = { address = vars.lanGateway; interface = vars.vmLanInterface; };
     nameservers = [ vars.domainControllerIp ];
   };