* fix: update agent-detector import to v2 namespace

laravel/agent-detector v2.0 moved the AgentDetector class from the
AgentDetector\ namespace to Laravel\AgentDetector\. With composer.json
now requiring ^2.0, PHPStan failed in CI with "Call to static method
detect() on an unknown class AgentDetector\AgentDetector". The detect()
API and AgentResult::$isAgent are unchanged, so only the import needs
updating.

* ci: drop PHP 8.2 and Laravel 10 from supported versions

pest 4 requires PHP >=8.3 and pest-plugin-laravel 4 requires Laravel
>=11, so the PHP 8.2 and Laravel 10 test matrix cells could never
install their dependencies. Align the advertised support with what the
toolchain can actually run: bump php to ^8.3, drop illuminate/* ^10.0
and testbench ^8.0, trim the CI matrix, and update the README.