Expose each concert's redemption deadline via the voucher/event APIs

The value already lived in event_ticket_settings but only the derived
deadlinePassed boolean reached callers - guests and the PDF export
couldn't show *when* a deadline is, only whether it already passed.

Co-Authored-By: Claude Sonnet 5 <noreply@anthropic.com>

src/models/tickets/tickets.interface.ts

@@ -10,7 +10,7 @@
  *       enum: [ACTIVE, UNDONE]
  *     EligibleEvent:
  *       type: object
- *       required: [eventId, name, startDateTime, location, deadlinePassed, isFull, collectAddress, requireAddress]
+ *       required: [eventId, name, startDateTime, location, redemptionDeadline, deadlinePassed, isFull, collectAddress, requireAddress]
  *       properties:
  *         eventId:
  *           type: integer
@@ -23,6 +23,11 @@
  *           format: date-time
  *         location:
  *           type: string
+ *         redemptionDeadline:
+ *           type: string
+ *           format: date-time
+ *           nullable: true
+ *           description: null when the event has no redemption deadline set
  *         deadlinePassed:
  *           type: boolean
  *         isFull:
@@ -224,6 +229,7 @@ export interface EligibleEvent {
 	name: string;
 	startDateTime: Date;
 	location: string;
+	redemptionDeadline: Date | null;
 	deadlinePassed: boolean;
 	isFull: boolean;
 	spotsRemaining: number | null;