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

home.nix

@@ -70,6 +70,16 @@
     initContent = ''
       export SHELL=$(which zsh)
       alias nix-shell='nix-shell --run $SHELL'
+
+      # Auto-update nixpkgs-unstable (for claude-code) on rebuild
+      nixos-rebuild() {
+        if [[ "$1" == "switch" || "$1" == "boot" || "$1" == "test" ]]; then
+          echo "Updating nixpkgs-unstable for latest Claude Code..."
+          nix flake update nixpkgs-unstable --flake /home/l-wyatt/Documents/nixos-configuration
+        fi
+        command sudo nixos-rebuild "$@" --flake /home/l-wyatt/Documents/nixos-configuration
+      }
+
       nix() {
         if [[ $1 == "develop" ]]; then
           shift