feat: auto-update Claude Code from nixpkgs-unstable

- Add nixpkgs-unstable input for latest Claude Code versions
- Remove duplicate home-manager config from configuration.nix (handled by flake)
- Remove fetchTarball/fetchGit calls incompatible with pure flake mode
- Add shell function to auto-update unstable on nixos-rebuild

flake.nix

@@ -3,6 +3,7 @@
 
   inputs = {
     nixpkgs.url = "github:nixos/nixpkgs/nixos-25.11";
+    nixpkgs-unstable.url = "github:nixos/nixpkgs/nixpkgs-unstable";
     home-manager = {
       url = "github:nix-community/home-manager/release-25.11";
       inputs.nixpkgs.follows = "nixpkgs";
@@ -10,17 +11,25 @@
     kickstart-nvim.url = "github:0xWheatyz/kickstart.nvim";
   };
 
-  outputs = { self, nixpkgs, home-manager, kickstart-nvim, ... }: {
+  outputs = { self, nixpkgs, nixpkgs-unstable, home-manager, kickstart-nvim, ... }:
+    let
+      system = "x86_64-linux";
+      pkgs-unstable = import nixpkgs-unstable {
+        inherit system;
+        config.allowUnfree = true;
+      };
+    in {
     nixosConfigurations = {
       nixos = nixpkgs.lib.nixosSystem {
-        system = "x86_64-linux";
+        inherit system;
+        specialArgs = { inherit pkgs-unstable; };
         modules = [
           ./configuration.nix
           home-manager.nixosModules.home-manager
           {
             home-manager.useGlobalPkgs = true;
             home-manager.useUserPackages = true;
-            home-manager.users.l-wyatt = import /home/l-wyatt/.config/home-manager/home.nix;
+            home-manager.users.l-wyatt = import ./home.nix;
             home-manager.extraSpecialArgs = {
               inherit kickstart-nvim;
             };