Add a per-event walk-in price and a POS tender to the door screen.

Events can now set an optional walk-in price (events.walk_in_price):
null falls back to the ticket price, 0 is a free walk-in. It is set in
the Create/Edit Event modal (EN/ES) and carried through create, update
and duplicate, but it is internal: public event responses and the
attendee-facing ticket/dashboard endpoints drop it, and only admin,
organizer and staff callers receive it.

The door screen no longer trusts the amount the client sends. It sends
a quantity and the server prices the charge from the event record:
walk-ins pay the walk-in price, existing tickets the ticket price. A
typed amount is only honoured with amountOverride from admin/organizer
and is written to audit_logs in the same transaction. The charged
amount stays snapshotted on the payment row.

POS is a new door tender for the physical card terminal. Staff pick
POS, see the amount to key in, charge the card, then confirm with
"Mark as paid"; it is then recorded like any other door payment
(provider and method 'pos'). It can be switched off globally or per
event via payment options, and shows up in the payments filters,
bookings, revenue summaries and door takings. PosChargePanel is where
an automatic terminal push would go later; nothing calls a terminal
today.

tickets.booking_source (online | walk_in | admin) records how a booking
was made. The migration backfills walk-ins from the door screen's
idempotency records; everything else stays online.

Co-Authored-By: Claude Opus 5.5 <noreply@anthropic.com>

frontend/src/app/admin/payment-options/page.tsx

@@ -42,6 +42,7 @@ export default function PaymentOptionsPage() {
     bankNotesEs: null,
     lightningEnabled: true,
     cashEnabled: true,
+    posEnabled: true,
     cashInstructions: null,
     cashInstructionsEs: null,
     allowDuplicateBookings: false,
@@ -83,6 +84,9 @@ export default function PaymentOptionsPage() {
     setOptions((prev) => ({ ...prev, [key]: value }));
   };
 
+  // Stored as 0/1 on Postgres; on unless explicitly switched off.
+  const posEnabled = !!(options.posEnabled ?? true);
+
   if (loading) {
     return (
       <div className="flex items-center justify-center min-h-[400px]">
@@ -424,6 +428,39 @@ export default function PaymentOptionsPage() {
         </div>
       </Card>
 
+      {/* POS terminal at the door */}
+      <Card className="mb-6">
+        <div className="p-6">
+          <div className="flex items-center justify-between">
+            <div className="flex items-center gap-3">
+              <div className="w-10 h-10 bg-violet-100 rounded-full flex items-center justify-center">
+                <CreditCardIcon className="w-5 h-5 text-violet-600" />
+              </div>
+              <div>
+                <h3 className="font-semibold text-lg">POS</h3>
+                <p className="text-sm text-gray-500">
+                  {locale === 'es'
+                    ? 'Terminal de tarjetas en la puerta. Solo en el Escáner; el personal confirma el pago manualmente.'
+                    : 'Card terminal at the door. Scanner only; staff confirm the payment by hand.'}
+                </p>
+              </div>
+            </div>
+            <button
+              onClick={() => updateOption('posEnabled', !posEnabled)}
+              className={`relative inline-flex h-6 w-11 flex-shrink-0 items-center rounded-full transition-colors ${
+                posEnabled ? 'bg-primary-yellow' : 'bg-gray-300'
+              }`}
+            >
+              <span
+                className={`inline-block h-4 w-4 transform rounded-full bg-white transition-transform ${
+                  posEnabled ? 'translate-x-6' : 'translate-x-1'
+                }`}
+              />
+            </button>
+          </div>
+        </div>
+      </Card>
+
       {/* Booking Settings */}
       <Card className="mb-6">
         <div className="p-6">
@@ -531,6 +568,16 @@ export default function PaymentOptionsPage() {
                 {locale === 'es' ? 'Efectivo' : 'Cash'}
               </span>
             </div>
+            <div className="flex items-center gap-2">
+              {posEnabled ? (
+                <CheckCircleIcon className="w-5 h-5 text-green-500" />
+              ) : (
+                <XCircleIcon className="w-5 h-5 text-gray-300" />
+              )}
+              <span className={posEnabled ? 'text-gray-900' : 'text-gray-400'}>
+                POS
+              </span>
+            </div>
           </div>
         </div>
       </Card>