Add read receipts and editing limits

Introduced message read tracking with a dedicated MessageReadingService, SignalR read request/response contracts, and hub notification flow for read receipts. Added configurable message edit constraints through MessageEditingOptions and a shared INowDateTimeProvider so timestamps are consistent across the app. Also fixed recipient validation in message removal and improved push token upsert behavior by matching the correct user/session record.

Govor.API/Hubs/Infrastructure/ChatHubConstants.cs

@@ -5,8 +5,9 @@ public static class ChatHubConstants
     public const string ReceiveMessage = "ReceiveMessage";
     public const string MessageSent = "MessageSent";
     public const string MessageRemoved = "MessageRemoved";
-    public const string MessageEdited = "MessageEdit";
-    
+    public const string MessageEdited = "MessageEdited";
+    public static string MessageRead = "MessageReaded";
+
     public static string GetUserGroup(Guid userId) => userId.ToString();
     public static string GetChatGroup(Guid groupId) => $"group_{groupId}";
     public static string GetPrivateChat(Guid groupId) => $"private_{groupId}";

Govor.API/Hubs/Infrastructure/ChatNotificationService.cs

@@ -45,6 +45,16 @@ public class ChatNotificationService : IChatNotificationService
        //     .SendAsync(ChatHubConstants.MessageSent, message);
     }
 
+    public async Task NotifyMessageWasReadAsync(MessageReadResponse response)
+    {
+        await NotifyParticipantsAsync(
+            response.ReaderId, 
+            response.RecipientId, 
+            response.RecipientType, 
+            ChatHubConstants.MessageRead, 
+            response);
+    }
+
     private async Task NotifyMessageReceivedInPrivateChatAsync(UserMessageResponse message)
     {
         

Govor.API/Hubs/Infrastructure/IChatNotificationService.cs

@@ -5,6 +5,7 @@ namespace Govor.API.Hubs.Infrastructure;
 public interface IChatNotificationService
 {
     Task NotifyMessageSentAsync(UserMessageResponse message);
+    Task NotifyMessageWasReadAsync(MessageReadResponse response);
     Task NotifyMessageRemovedAsync(MessageRemovedResponse response);
     Task NotifyMessageEditedAsync(MessageEditResponse response);
 }