Add unit tests and implement group repository interfaces

Introduces comprehensive unit tests for MessageService covering send, edit, and delete message scenarios. Adds and implements IGroupsRepository, IGroupsReader, and IGroupsWriter interfaces with method stubs in GroupRepository. Updates ChatGroup model with Description and ImageId fields, and registers GroupRepository in DI. Fixes parameter order in SendMessage record.

Govor.Core/Models/ChatGroup.cs

@@ -4,6 +4,9 @@ public class ChatGroup
 {
     public Guid Id { get; set; }
     public string Name { get; set; }
+    public string Description { get; set; }
+    public Guid ImageId { get; set; }
+    
     public List<string> InviteCode { get; set; }
     public bool IsChannel { get; set; }
     public bool IsPrivate { get; set; }