feat(build): Add in nix flake for devShell

- Flake.nix and lock for devShell
- .envrc for direnv
- Ignore .direnv folder

Author: Uzaaft

.envrc

@@ -0,0 +1,4 @@
+# vim: set ft=bash:
+if has nix; then
+  use flake
+fi

.gitignore

@@ -22,3 +22,4 @@ pnpm-debug.log*
 # macOS-specific files
 .DS_Store
 .vercel
+.direnv

flake.lock

@@ -0,0 +1,24 @@
+{
+  description = "docs.astronvim.org";
+  inputs.nixpkgs.url = "github:NixOS/nixpkgs/nixpkgs-unstable";
+  inputs.systems.url = "github:nix-systems/default";
+  inputs.flake-utils = {
+    url = "github:numtide/flake-utils";
+    inputs.systems.follows = "systems";
+  };
+
+  outputs = {
+    nixpkgs,
+    flake-utils,
+    ...
+  }:
+    flake-utils.lib.eachDefaultSystem (
+      system: let
+        pkgs = nixpkgs.legacyPackages.${system};
+      in {
+        devShells.default = pkgs.mkShell {packages = with pkgs; [nodejs_22 pnpm alejandra];};
+
+        formatter = pkgs.alejandra;
+      }
+    );
+}