feat: Add go package and set as default output

Adds a new `go` package to the flake and sets it as the default output. This allows users to easily access the Go development environment.
---
{"auto-commit-msg":{"language":"rust","version":"0.4.0-dev","model":"gemini-2.5-flash-lite","response_time":1.32,"execution_time":1.35}}

Author: sestrella

flake.nix

@@ -34,7 +34,8 @@
           };
         in
         {
-          default = pkgs.callPackage ./default.nix { };
+          default = self.packages.${system}.go;
+          go = pkgs.callPackage ./default.nix { };
           rust = pkgs.callPackage ./rust/default.nix { };
         }
       );