monitoring: add nixos-exporter to monitoring01

Enable the nixos-exporter prometheus exporter with flake collector
to track NixOS generation metrics and flake revision status.

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

flake.nix

@@ -17,6 +17,10 @@
       url = "git+https://git.t-juice.club/torjus/labmon?ref=master";
       inputs.nixpkgs.follows = "nixpkgs-unstable";
     };
+    nixos-exporter = {
+      url = "git+https://git.t-juice.club/torjus/nixos-exporter";
+      inputs.nixpkgs.follows = "nixpkgs-unstable";
+    };
   };
 
   outputs =
@@ -27,6 +31,7 @@
       sops-nix,
       alerttonotify,
       labmon,
+      nixos-exporter,
       ...
     }@inputs:
     let
@@ -180,6 +185,7 @@
             ./hosts/monitoring01
             sops-nix.nixosModules.sops
             labmon.nixosModules.labmon
+            nixos-exporter.nixosModules.default
           ];
         };
         jelly01 = nixpkgs.lib.nixosSystem {