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>

flake.nix

@@ -200,6 +200,15 @@
             ./hosts/monitoring02
           ];
         };
+        nix-cache02 = nixpkgs.lib.nixosSystem {
+          inherit system;
+          specialArgs = {
+            inherit inputs self;
+          };
+          modules = commonModules ++ [
+            ./hosts/nix-cache02
+          ];
+        };
       };
       packages = forAllSystems (
         { pkgs }: