feat(nix-cache): authorize pve1's wayne key as remote builder client

Generated /home/wayne/.ssh/id_ed25519 on pve1 (single-user Nix install
owned by wayne, no daemon — builds run as wayne not root). Adds the
public key to remoteBuilderAuthorizedKeys so nix-cache accepts it.

After deploying nix-cache, re-run configure-nix-cache-client.sh as
wayne on pve1 to wire in the builder line and known_hosts entry.

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

variables.nix

@@ -58,6 +58,7 @@
     "ssh-ed25519 AAAAC3NzaC1lZDI1NTE5AAAAIBZ9WKKAlP9Z7GQdgaZ1Xgw9C+vja2lqEZO5rJFpVqYN root@ha-server-1"
     "ssh-ed25519 AAAAC3NzaC1lZDI1NTE5AAAAIEGNKlaaMckd8nLWNGz4B2QokXjnnIvM+rEUv+R6h0sp root@ha-server-2"
     "ssh-ed25519 AAAAC3NzaC1lZDI1NTE5AAAAIK+XeMco7OxUpjrjZm54HogMs9QB5xlcKmElASRvrmlW root@nixos"
+    "ssh-ed25519 AAAAC3NzaC1lZDI1NTE5AAAAIMseQwPpmaa6cgV5U8KhUsiVSYARG85zGa9rho0LJWks wayne@pve1"
   ];
 
   # Admin SSH public key, authorized on the primary user of every host and