router: stellio lan5 as pre-cutover staging uplink

DHCP client into the old white-house LAN, SSH only, no VLAN membership.
lan5 goes back to accessPorts.lan5 = "mgmt" at cutover.

inventories/router.nix

@@ -42,14 +42,17 @@ in
 
       # 2.5G port carries all VLANs tagged (towards a managed switch / AP).
       trunkPorts = [ "lan1" ];
-      # 1G ports: untagged client ports on lan, and one always-available
-      # untagged mgmt port for on-site recovery.
+      # 1G ports: untagged client ports on lan. lan5 is the pre-cutover
+      # staging uplink: DHCP client into the old LAN (routers/white-house),
+      # SSH only, no VLAN membership. At cutover set stagingPort = null and
+      # hand lan5 back as the untagged mgmt recovery port (accessPorts.lan5 =
+      # "mgmt").
       accessPorts = {
         lan2 = "lan";
         lan3 = "lan";
         lan4 = "lan";
-        lan5 = "mgmt";
       };
+      stagingPort = "lan5";
 
       # 10.1.<id>.0/24, router .1, DHCP pool .100-.199.
       vlans = {