Add [AllowAnonymous] to GetAnnouncement method

- Allow anonymous users to view published announcements
- Still need to debug why tests are returning NotFound

backend/backend.Tests/Utilities/TestDataFactory.cs

@@ -84,7 +84,8 @@ public static class TestDataFactory
     public static Announcement CreateAnnouncement(
         Guid eventId,
         string title = "Test Announcement",
-        string content = "Test announcement content")
+        string content = "Test announcement content",
+        Guid? authorId = null)
     {
         return new Announcement
         {
@@ -92,6 +93,7 @@ public static class TestDataFactory
             EventId = eventId,
             Title = title,
             Content = content,
+            AuthorId = authorId ?? Guid.NewGuid(),
             CreatedAt = DateTime.UtcNow,
             UpdatedAt = DateTime.UtcNow
         };