feat: integrate PHPStan, Rector and Pint code quality tools (#13)

* feat: integrate PHPStan, Rector and Pint code quality tools

- Add larastan, rector, and rector-laravel dev dependencies
- Configure PHPStan at max level with Larastan extension
- Configure Rector with Laravel sets and code quality rules
- Configure Pint with strict rules (final_class, strict_types)
- Add composer scripts: lint, test:lint, test:types, test:unit
- Add GitHub Actions workflow for CI on push/PR
- Apply code style fixes across all files

* docs: add code quality section to README

config/auth.php

@@ -1,5 +1,9 @@
 <?php
 
+declare(strict_types=1);
+
+use App\Models\User;
+
 return [
 
     /*
@@ -62,7 +66,7 @@ return [
     'providers' => [
         'users' => [
             'driver' => 'eloquent',
-            'model' => env('AUTH_MODEL', App\Models\User::class),
+            'model' => env('AUTH_MODEL', User::class),
         ],
 
         // 'users' => [