Fix cpx execution - #7

Summary

• make the Composer bin point to the source CLI entrypoint so cpx can execute dev/source installs
• load Composer's root autoloader when the raw bin is executed directly by cpx
• include runtime source files in Composer dist archives
• move laravel-zero/framework to runtime dependencies for source installs
• document cpx usage and add a CI cpx smoke test
• refresh composer.lock to a PHP 8.3-compatible dependency set so release PHAR builds can run on the existing workflow

Test Plan

• php -l unolia
• ./vendor/bin/pint --test
• composer test
• cpx unolia/unolia-cli:dev-fix/cpx-execution --version