Refactor, cleanup code and add documentaiton

Assets/Scripts/CardSystem/StateMachine/ICardStateDragHandler.cs

@@ -0,0 +1,20 @@
+namespace UI.CardSystem.StateMachine
+{
+    /// <summary>
+    /// Implement on a state component to receive routed drag events from Card.
+    /// Similar to ICardClickHandler but for drag behavior.
+    /// </summary>
+    public interface ICardStateDragHandler
+    {
+        /// <summary>
+        /// Called when drag starts. Return true to handle drag (prevent default DraggingState transition).
+        /// </summary>
+        bool OnCardDragStarted(CardContext context);
+        
+        /// <summary>
+        /// Called when drag ends. Return true to handle drag end (prevent default state transitions).
+        /// </summary>
+        bool OnCardDragEnded(CardContext context);
+    }
+}
+