Make expiryDate an internal concern, auto-set to event date + 7 days

The expiry date is no longer user-facing: it is removed from the API
(request and response) and the frontend. The backend now automatically
calculates it as the event date plus 7 days. The expired banner and
RSVP-bar filtering by expired status are also removed from the UI,
since expiry is purely an internal data-retention mechanism.

Co-Authored-By: Claude Opus 4.6 <noreply@anthropic.com>

backend/src/main/java/de/fete/adapter/in/web/EventController.java

@@ -20,9 +20,7 @@ import de.fete.domain.port.in.CreateEventUseCase;
 import de.fete.domain.port.in.CreateRsvpUseCase;
 import de.fete.domain.port.in.GetAttendeesUseCase;
 import de.fete.domain.port.in.GetEventUseCase;
-import java.time.Clock;
 import java.time.DateTimeException;
-import java.time.LocalDate;
 import java.time.ZoneId;
 import java.util.List;
 import java.util.UUID;
@@ -39,22 +37,19 @@ public class EventController implements EventsApi {
   private final CreateRsvpUseCase createRsvpUseCase;
   private final CountAttendeesByEventUseCase countAttendeesByEventUseCase;
   private final GetAttendeesUseCase getAttendeesUseCase;
-  private final Clock clock;
 
-  /** Creates a new controller with the given use cases and clock. */
+  /** Creates a new controller with the given use cases. */
   public EventController(
       CreateEventUseCase createEventUseCase,
       GetEventUseCase getEventUseCase,
       CreateRsvpUseCase createRsvpUseCase,
       CountAttendeesByEventUseCase countAttendeesByEventUseCase,
-      GetAttendeesUseCase getAttendeesUseCase,
-      Clock clock) {
+      GetAttendeesUseCase getAttendeesUseCase) {
     this.createEventUseCase = createEventUseCase;
     this.getEventUseCase = getEventUseCase;
     this.createRsvpUseCase = createRsvpUseCase;
     this.countAttendeesByEventUseCase = countAttendeesByEventUseCase;
     this.getAttendeesUseCase = getAttendeesUseCase;
-    this.clock = clock;
   }
 
   @Override
@@ -67,8 +62,7 @@ public class EventController implements EventsApi {
         request.getDescription(),
         request.getDateTime(),
         zoneId,
-        request.getLocation(),
-        request.getExpiryDate()
+        request.getLocation()
     );
 
     Event event = createEventUseCase.createEvent(command);
@@ -79,7 +73,6 @@ public class EventController implements EventsApi {
     response.setTitle(event.getTitle());
     response.setDateTime(event.getDateTime());
     response.setTimezone(event.getTimezone().getId());
-    response.setExpiryDate(event.getExpiryDate());
 
     return ResponseEntity.status(HttpStatus.CREATED).body(response);
   }
@@ -99,8 +92,6 @@ public class EventController implements EventsApi {
     response.setLocation(event.getLocation());
     response.setAttendeeCount(
         (int) countAttendeesByEventUseCase.countByEvent(eventToken));
-    response.setExpired(
-        event.getExpiryDate().isBefore(LocalDate.now(clock)));
 
     return ResponseEntity.ok(response);
   }

backend/src/main/java/de/fete/application/service/EventService.java

@@ -17,6 +17,8 @@ import org.springframework.stereotype.Service;
 @Service
 public class EventService implements CreateEventUseCase, GetEventUseCase {
 
+  private static final int EXPIRY_DAYS_AFTER_EVENT = 7;
+
   private final EventRepository eventRepository;
   private final Clock clock;
 
@@ -28,13 +30,7 @@ public class EventService implements CreateEventUseCase, GetEventUseCase {
 
   @Override
   public Event createEvent(CreateEventCommand command) {
-    if (!command.expiryDate().isAfter(LocalDate.now(clock))) {
-      throw new ExpiryDateInPastException(command.expiryDate());
-    }
-
-    if (!command.expiryDate().isAfter(command.dateTime().toLocalDate())) {
-      throw new ExpiryDateBeforeEventException(command.expiryDate(), command.dateTime());
-    }
+    LocalDate expiryDate = command.dateTime().toLocalDate().plusDays(EXPIRY_DAYS_AFTER_EVENT);
 
     var event = new Event();
     event.setEventToken(EventToken.generate());
@@ -44,7 +40,7 @@ public class EventService implements CreateEventUseCase, GetEventUseCase {
     event.setDateTime(command.dateTime());
     event.setTimezone(command.timezone());
     event.setLocation(command.location());
-    event.setExpiryDate(command.expiryDate());
+    event.setExpiryDate(expiryDate);
     event.setCreatedAt(OffsetDateTime.now(clock));
 
     return eventRepository.save(event);

backend/src/main/java/de/fete/domain/model/CreateEventCommand.java

@@ -10,6 +10,5 @@ public record CreateEventCommand(
     String description,
     OffsetDateTime dateTime,
     ZoneId timezone,
-    String location,
-    LocalDate expiryDate
+    String location
 ) {}

backend/src/main/resources/openapi/api.yaml

@@ -160,7 +160,6 @@ components:
         - title
         - dateTime
         - timezone
-        - expiryDate
       properties:
         title:
           type: string
@@ -181,11 +180,6 @@ components:
         location:
           type: string
           maxLength: 500
-        expiryDate:
-          type: string
-          format: date
-          description: Date after which event data is deleted. Must be in the future.
-          example: "2026-06-15"
 
     CreateEventResponse:
       type: object
@@ -195,7 +189,6 @@ components:
         - title
         - dateTime
         - timezone
-        - expiryDate
       properties:
         eventToken:
           type: string
@@ -218,10 +211,6 @@ components:
           type: string
           description: IANA timezone of the organizer
           example: "Europe/Berlin"
-        expiryDate:
-          type: string
-          format: date
-          example: "2026-06-15"
 
     GetEventResponse:
       type: object
@@ -231,7 +220,6 @@ components:
         - dateTime
         - timezone
         - attendeeCount
-        - expired
       properties:
         eventToken:
           type: string
@@ -264,10 +252,6 @@ components:
           minimum: 0
           description: Number of confirmed attendees (attending=true)
           example: 12
-        expired:
-          type: boolean
-          description: Whether the event's expiry date has passed
-          example: false
 
     CreateRsvpRequest:
       type: object