hosts: add nix-cache02 build host

New build host to replace nix-cache01 with:
- 8 CPU cores, 16GB RAM, 200GB disk
- Static IP 10.69.13.25

Co-Authored-By: Claude Opus 4.5 <noreply@anthropic.com>

hosts/nix-cache02/default.nix

@@ -0,0 +1,5 @@
+{ ... }: {
+  imports = [
+    ./configuration.nix
+  ];
+}