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

database/migrations/0001_01_01_000000_create_users_table.php

@@ -1,5 +1,7 @@
 <?php
 
+declare(strict_types=1);
+
 use Illuminate\Database\Migrations\Migration;
 use Illuminate\Database\Schema\Blueprint;
 use Illuminate\Support\Facades\Schema;
@@ -11,7 +13,7 @@ return new class extends Migration
      */
     public function up(): void
     {
-        Schema::create('users', function (Blueprint $table) {
+        Schema::create('users', function (Blueprint $table): void {
             $table->id();
             $table->string('name');
             $table->string('email')->unique();
@@ -21,13 +23,13 @@ return new class extends Migration
             $table->timestamps();
         });
 
-        Schema::create('password_reset_tokens', function (Blueprint $table) {
+        Schema::create('password_reset_tokens', function (Blueprint $table): void {
             $table->string('email')->primary();
             $table->string('token');
             $table->timestamp('created_at')->nullable();
         });
 
-        Schema::create('sessions', function (Blueprint $table) {
+        Schema::create('sessions', function (Blueprint $table): void {
             $table->string('id')->primary();
             $table->foreignId('user_id')->nullable()->index();
             $table->string('ip_address', 45)->nullable();