Add JSON files for Payment Gateway Interface and API documentation updates

- Created a new JSON file for the PaymentGatewayInterface.php, detailing its methods and return types.
- Added a JSON file for payment.md, documenting various API endpoints and their parameters, responses, and errors.
- Introduced a JSON file for fix-admin-modal-and-calendar.md, outlining issues and solutions related to admin modal and calendar functionalities.

assets/admin/pages/StaffPage.tsx

@@ -168,7 +168,7 @@ export default function StaffPage() {
 
       {/* KPI bar */}
       {!isLoading && (
-        <div className="stat-grid" style={{ marginBottom: 16, gridTemplateColumns: 'repeat(3, 1fr)' }}>
+        <div className="stat-grid" style={{ marginBottom: 16 }}>
           <div className="card card-pad" style={{ textAlign: 'center' }}>
             <div style={{ fontSize: 28, fontWeight: 800, color: 'var(--text-1)' }}>{total}</div>
             <div style={{ fontSize: 13, color: 'var(--text-3)', marginTop: 2 }}>کل پرسنل</div>