add nix development environment

Provide a direnv-loaded Laravel and future Vue toolchain with isolated worktree ports and a process-compose stack. Use PostgreSQL for local runtime services while retaining in-memory SQLite for PHPUnit.

flake.nix

@@ -0,0 +1,54 @@
+{
+  inputs = {
+    nixpkgs.url = "github:NixOS/nixpkgs/nixos-unstable";
+    utils.url = "github:numtide/flake-utils";
+  };
+
+  outputs =
+    {
+      self,
+      nixpkgs,
+      utils,
+    }:
+    utils.lib.eachDefaultSystem (
+      system:
+      let
+        pkgs = nixpkgs.legacyPackages.${system};
+        php = pkgs.php.buildEnv {
+          extraConfig = ''
+            memory_limit = "1G";
+            upload_max_filesize = "10M";
+            post_max_size = "25M";
+          '';
+        };
+      in
+      {
+        formatter = pkgs.nixfmt-tree;
+
+        devShells.default = pkgs.mkShell {
+          packages = with pkgs; [
+            bash
+            onefetch
+            just
+            php
+            phpPackages.composer
+            phpPackages.php-codesniffer
+            vscode-langservers-extracted
+            nodejs
+            nixfmt
+            nixfmt-tree
+            cypress
+            yaml-language-server
+            typescript
+            postgresql
+            mailpit
+            process-compose
+            mkcert
+            caddy
+          ];
+
+          shellHook = builtins.readFile ./nix/shell-hook.sh;
+        };
+      }
+    );
+}