Tell harness branch configuration

<?php
require 'examples/boot.php';
require_once dirname(__DIR__).'/Support.php';

use Cognesy\Tell\Tell;

$project = TellHarnessExample::project();

try {
    $tell = Tell::open($project);
    $workspace = $tell->workspace();
    $workspace->initialize();
    $workspace->branches()->create('review', empty: true);

    $config = $workspace->configuration('review');
    $initial = $config->show();
    $model = $config->set('model', 'deepseek-v4-flash', $initial->version);
    $policy = $config->set('timeoutMs', 15_000, $model->version);
    $effective = $config->effective();

    echo 'Configured branch: '.$effective->branch."\n";
    echo 'Model source: '.$effective->provenance['model']."\n";
    echo 'Timeout: '.$effective->values['timeoutMs']."ms\n";

    // Delete must use the most recently observed version as well.
    $config->delete('timeoutMs', $policy->version);

    assert($effective->values['model'] === 'deepseek-v4-flash');
    assert($effective->provenance['timeoutMs'] === 'branch');
} finally {
    TellHarnessExample::remove($project);
}