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

phpstan.neon

@@ -0,0 +1,21 @@
+includes:
+    - vendor/larastan/larastan/extension.neon
+    - vendor/nesbot/carbon/extension.neon
+    - phar://phpstan.phar/conf/bleedingEdge.neon
+
+parameters:
+
+    paths:
+        - app
+        - bootstrap/app.php
+        - config
+        - database
+        - public
+        - routes
+
+    excludePaths:
+        - config/database.php
+
+    level: max
+
+    tmpDir: /tmp/phpstan