Add treefmt-nix for formatting all the files

flake.nix

@@ -133,6 +133,12 @@
         utils.follows = "flake-utils";
       };
     };
+
+    treefmt-nix = {
+      type = "github";
+      owner = "numtide";
+      repo = "treefmt-nix";
+    };
   };
   outputs = {
     self,
@@ -153,6 +159,7 @@
       systems = flake-utils.lib.defaultSystems;
       imports = [
         inputs.home-manager.flakeModules.home-manager
+        inputs.treefmt-nix.flakeModule
         nixos
         home
         deploy
@@ -169,7 +176,6 @@
             allowUnfree = true;
           };
         };
-        formatter = pkgs.alejandra;
         packages = import ./pkgs (
           args
           // {
@@ -185,6 +191,40 @@
             nvfetcher
           ];
         };
+        treefmt = {
+          programs = {
+            alejandra = {
+              enable = true;
+              excludes = ["pkgs/_sources/*.nix"];
+            };
+            biome = {
+              enable = true;
+              includes = ["*.json"];
+              excludes = ["pkgs/_sources/*.json"];
+              settings = {
+                javascript.formatter.enabled = false;
+                css.formatter.enabled = false;
+              };
+            };
+            dprint = {
+              enable = true;
+              includes = ["*.md" "*.toml" "*.yaml"];
+              excludes = ["secrets/*.yaml"];
+              settings = {
+                plugins = pkgs.dprint-plugins.getPluginList (plugins:
+                  with plugins; [
+                    dprint-plugin-toml
+                    dprint-plugin-markdown
+                    g-plane-pretty_yaml
+                  ]);
+              };
+            };
+            just = {
+              enable = true;
+              includes = [".justfile"];
+            };
+          };
+        };
       };
       flake = {
         overlays = {