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/backend.Tests/Controllers/DashboardControllerTests.cs

@@ -155,15 +155,13 @@ public class DashboardControllerTests : IDisposable
             organizerId: organizer.Id,
             status: EventStatus.Completed);
 
-        _context.Events.AddRange(upcomingEvent, pastEvent);
+        var cancelledEvent = TestDataFactory.CreateEvent(name: "Cancelled Event", organizerId: organizer.Id, status: EventStatus.Published);
+        _context.Events.AddRange(upcomingEvent, pastEvent, cancelledEvent);
         await _context.SaveChangesAsync();
 
         var upcomingReg = TestDataFactory.CreateRegistration(upcomingEvent.Id, participant.Id, RegistrationStatus.Confirmed);
         var pastReg = TestDataFactory.CreateRegistration(pastEvent.Id, participant.Id, RegistrationStatus.Completed);
-        var cancelledReg = TestDataFactory.CreateRegistration(
-            TestDataFactory.CreateEvent(name: "Cancelled Event", organizerId: organizer.Id, status: EventStatus.Published).Id,
-            participant.Id,
-            RegistrationStatus.Cancelled);
+        var cancelledReg = TestDataFactory.CreateRegistration(cancelledEvent.Id, participant.Id, RegistrationStatus.Cancelled);
         _context.Registrations.AddRange(upcomingReg, pastReg, cancelledReg);
         await _context.SaveChangesAsync();