Track nix-cache's real deployment as lxc-nix-cache, not proxmox-nix-cache

The old proxmox-nix-cache VM was destroyed and nix-cache is being
redeployed as an LXC container going forward. Without this update,
create-proxmox-resource.sh's duplicate-host check (which only reads this
static list, not live Proxmox state) kept refusing to create
lxc-nix-cache even though nothing named nix-cache actually exists on the
node anymore.

Co-Authored-By: Claude Sonnet 5 <noreply@anthropic.com>

README.md

@@ -21,7 +21,7 @@ list:
 | `linode-minimal` | Minimal NixOS host profile on a Linode VPS (real, deployed) |
 | `proxmox-minimal` | Minimal NixOS host profile on Proxmox (real, deployed — previously the flat `nix-minimal` target) |
 | `lxc-minimal` | Minimal NixOS host profile in a Proxmox LXC container |
-| `linode-nix-cache` / `proxmox-nix-cache` / `lxc-nix-cache` | Local Nix binary cache and remote builder (`proxmox-nix-cache` is the real, deployed one — previously the flat `nix-cache` target) |
+| `linode-nix-cache` / `proxmox-nix-cache` / `lxc-nix-cache` | Local Nix binary cache and remote builder (`lxc-nix-cache` is the real, deployed one — previously `proxmox-nix-cache`, itself previously the flat `nix-cache` target) |
 | `linode-server` / `proxmox-server` / `lxc-server` | Storage, NFS, backup, and monitoring exporter host (`proxmox-server` is the real, deployed one — previously the flat `server` target) |
 | `linode-docker` / `proxmox-docker` / `lxc-docker` | Docker host for the main container stack (`proxmox-docker` is the real, deployed one — previously the flat `docker` target) |
 | `linode-gui` / `proxmox-gui` / `lxc-gui` | Cinnamon desktop workstation (`proxmox-gui` is the real, deployed one — previously the flat `nixos` target) |

variables.nix

@@ -166,7 +166,7 @@
   deployedTargets = [
     "linode-minimal"
     "proxmox-minimal"
-    "proxmox-nix-cache"
+    "lxc-nix-cache"
     "proxmox-server"
     "proxmox-docker"
     "proxmox-gui"