feat(Core): update DTOs and shared models

FinlyticCore/Models/Trades/CloseTradeRequest.cs

@@ -0,0 +1,13 @@
+using System;
+
+namespace FinlyticCore.Models.Trades;
+
+/// <summary>
+/// Request payload for manually closing an active trade via REST API.
+/// </summary>
+public class CloseTradeRequest
+{
+    public decimal UserExitPrice { get; set; }
+    public DateTime? UserExitTimestamp { get; set; }
+    public string CloseReason { get; set; } = "ManualClosure"; // "TakeProfitHit", "StopLossHit", "ManualClosure", "TimeExpired"
+}