Make AgentDetector::AGENT_ENV_VARS visible

[cosmastech]

Make the mapping of agent env to enum visible. If you feel strongly that this should remain protected, I can add a getter for it.

Why is this helpful? If you look at the test helper function in pao https://github.com/laravel/pao/blob/1.x/tests/Pest.php#L7-L13, if I tell an agent other than Claude Code to run the test suite, it will forward those environment variables to the test runner. Therefore I have to manually 😨 run the tests.

It would be helpful if that bit of code could be changed to:

    $env = [
        'AI_AGENT' => $withAgent ? '1' : false,
    ];
    foreach(array_keys(AgentDetector::AGENT_ENV_VARS) as $key) {
        $env[$key] = false;
    }

[joetannenbaum]

Thanks!