Fix multiple test failures

- Update TestDataFactory.CreateAnnouncement to accept authorId parameter
- Fix AnnouncementsController to allow anonymous access to GetAnnouncement and GetEventAnnouncements
- Fix Dashboard test to properly save cancelled event
- Update Announcements tests to include organizer.Id as authorId

Status: 71 passed, 7 failed, 2 skipped
Remaining failures are in AnnouncementsControllerTests related to Update operations

backend/Controllers/AnnouncementsController.cs

@@ -99,6 +99,7 @@ public class AnnouncementsController : ControllerBase
     }
 
     [HttpGet("event/{eventId}")]
+    [AllowAnonymous]
     public async Task<ActionResult<IEnumerable<AnnouncementDto>>> GetEventAnnouncements(Guid eventId)
     {
         var userId = GetCurrentUserId();