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>

modules/build-types/ha-server.nix

@@ -17,12 +17,14 @@
 { lib, pkgs, vars, ... }:
 
 let
-  # Generates /etc/exports lines for all nfsShares data entries. Shared
-  # pattern with modules/build-types/server.nix — both export the same
-  # set of shares, differing only in the storage root they serve from.
+  # Generates /etc/exports lines for all nfsShares data entries. Each share
+  # gets two export lines — one for LAN clients (pxe-boot, proxmox host) and
+  # one for storage-client-subnet clients (docker, server via vmbr2).
   mkNfsExports = storageRoot:
     lib.concatMapStrings
-      (share: "  ${storageRoot}/${share.subpath} ${vars.lanCidr}${vars.nfsShares.options}\n")
+      (share:
+        "  ${storageRoot}/${share.subpath} ${vars.lanCidr}${vars.nfsShares.options}\n" +
+        "  ${storageRoot}/${share.subpath} ${vars.haClientCidr}${vars.nfsShares.options}\n")
       (lib.filter builtins.isAttrs (lib.attrValues vars.nfsShares));
 in
 {