ci: Add GitHub Actions CI workflow for automated testing and code quality #80

Summary

The repository currently has a comprehensive suite of backend (PHPUnit) and frontend (Node) tests, as well as code formatting checks (Laravel Pint), but lacks an automated CI (Continuous Integration) workflow. As a result, pull requests and commits are not automatically tested or verified before merging.

Proposed Solution

Set up a GitHub Actions workflow (.github/workflows/ci.yml) triggered on push (main/master branches) and pull_request:

1. PHP / Laravel Backend Pipeline:

   • Setup PHP 8.3 with required extensions (sqlite, mbstring, pdo_sqlite, xml).
   • Cache Composer dependencies.
   • Run Laravel Pint code style check (./vendor/bin/pint --test).
   • Run PHPUnit test suites (php artisan test / ./vendor/bin/phpunit).

2. Frontend & Assets Pipeline:

   • Setup Node.js.
   • Cache npm dependencies.
   • Run frontend tests (npm run test:frontend).
   • Run production asset build check (npm run build).

Expected Impact

• Automated regression testing on every PR and commit.
• Consistent code formatting enforcement via Pint.
• Improved stability for contest engine and web platform.