feat: add role-based authentication support and update UI toggle label to Agent

lib/features/auth/presentation/widgets/role_toggle.dart

@@ -23,7 +23,7 @@ class RoleToggle extends StatelessWidget {
         mainAxisSize: MainAxisSize.min,
         children: [
           _buildToggleButton('User', 'USER'),
-          _buildToggleButton('Admin', 'AGENT'),
+          _buildToggleButton('Agent', 'AGENT'),
         ],
       ),
     );