fix: show Pay Now button and modal during impersonation

Remove readOnly guard from Pay Now button and PaymentModal in BillingPayments.
The readOnly guard was too broad — it hid the Pay Now button during staff
impersonation sessions, making it impossible for staff to collect payments.

Other readOnly guards (Remove payment method, Autopay toggle) remain intact.

Co-Authored-By: Paperclip <noreply@paperclip.ing>

apps/web/src/portal/sections/BillingPayments.tsx

@@ -110,14 +110,12 @@ export function BillingPayments({ sessionId, readOnly }: BillingPaymentsProps) {
               {pending.length} unpaid invoice{pending.length > 1 ? "s" : ""}
             </p>
           </div>
-          {!readOnly && (
             <button
               onClick={() => setShowPaymentModal(true)}
               className="px-6 py-2 bg-(--color-accent) text-white rounded-lg text-sm font-medium hover:bg-(--color-accent-hover)"
             >
               Pay Now
             </button>
-          )}
         </div>
       )}
 
@@ -293,7 +291,7 @@ export function BillingPayments({ sessionId, readOnly }: BillingPaymentsProps) {
       )}
 
       {/* Payment Modal */}
-      {showPaymentModal && !readOnly && (
+      {showPaymentModal && (
         <PaymentModal
           pending={pending}
           totalPending={totalPending}