rework messages

+ addition LocalStorageService
+ tests

Govor.Core/Models/MessageReaction.cs

@@ -0,0 +1,15 @@
+namespace Govor.Core.Models;
+
+public class MessageReaction
+{
+    public Guid Id { get; set; }
+    
+    public Guid MessageId { get; set; }
+    public Message Message { get; set; }
+
+    public Guid UserId { get; set; }
+    public User User { get; set; } 
+    
+    public string ReactionCode { get; set; } // "❤️", "🔥", "👍", ":custom_emoji:" 
+    public DateTime ReactedAt { get; set; } = DateTime.UtcNow;
+}