feat(nix): add style tooling

flake.nix

@@ -62,6 +62,12 @@
       inputs.nixpkgs.follows = "nixpkgs";
     };
 
+    # Repository formatter and Nix lint wiring.
+    treefmt-nix = {
+      url = "github:numtide/treefmt-nix";
+      inputs.nixpkgs.follows = "nixpkgs";
+    };
+
     # CachyOS kernel and binary cache.
     # This must not follow this flake's nixpkgs because Chaotic builds against its own pinned package set.
     # Its cache serves the kernel only when the overlay stays on the cache-friendly path.
@@ -70,11 +76,10 @@
 
   outputs =
     { self, nixpkgs, ... }@inputs:
-    {
-      nixosConfigurations = (import ./src/dotfiles {
-        inherit inputs self;
-        lib = nixpkgs.lib;
-        root = ./configs/nixos;
-      }).nixosConfigurations;
+    import ./src/dotfiles {
+      inherit inputs self;
+      lib = nixpkgs.lib;
+      root = ./configs/nixos;
+      system = "x86_64-linux";
     };
 }