Add disbursement support, webhook verification, and CI

[MrOne-inc]

Summary

• Disbursement support: New Payout and PayoutBuilder classes with fluent API for mobile money and bank payouts, plus mobileMoneyPayout(), bankPayout(), findPayout(), payouts(), and payoutFee() methods on the Snippe client
• Webhook signature verification: HMAC-SHA256 verification via isValid($secret) and verify($secret) methods on the Webhook class — prevents accepting forged webhook events
• Payout webhook events: Added isPayoutCompleted() and isPayoutFailed() helpers
• GitHub Actions CI: Automated test suite running on PHP 8.1, 8.2, 8.3, and 8.4

Usage examples

Payouts

// Mobile money payout
$payout = $snippe->mobileMoneyPayout(5000, '0754123456', 'John Doe')
    ->narration('Salary payment')
    ->webhook('https://yoursite.com/webhook')
    ->send();

echo $payout->reference(); // "667c9279-..."
echo $payout->fees();      // fee amount

// Bank payout
$payout = $snippe->bankPayout(10000, 'CRDB', '0200000000', 'Jane Smith')
    ->narration('Invoice payment')
    ->send();

// Check fee before sending
$fee = $snippe->payoutFee(5000);

Webhook signature verification

$event = Webhook::capture();
$event->verify('your_webhook_secret'); // throws SnippeException if invalid

if ($event->isPayoutCompleted()) {
    // handle payout completion
}

Test plan

• All 66 tests pass (166 assertions) — ran locally on PHP 8.2
• CI should run automatically on this PR
• Verify payout endpoints with live API key