Add formatter for codebase

flake.nix

@@ -24,5 +24,6 @@
     in {
       devShells.default = import ./shell.nix { inherit pkgs; };
 
+      formatter = pkgs.treefmt;
     });
 }

treefmt.toml

@@ -0,0 +1,24 @@
+[formatter.nix]
+command = "nixpkgs-fmt"
+includes = ["*.nix"]
+
+[formatter.ruby]
+command = "rufo"
+options = ["-x"]
+includes = ["*.rb"]
+
+[formatter.web]
+command = "prettier"
+options = ["--write"]
+includes = [
+ "*.css",
+ "*.html",
+ "*.js",
+ "*.json",
+ "*.jsx",
+ "*.md",
+ "*.mdx",
+ "*.scss",
+ "*.ts",
+ "*.yaml",
+]