Unity U3: Add CoachResponse.cs (#48)

This class maps to the response of the POST /api/coach/chat endpoint, including properties for reply, deck report, and suggestions.

unity-client/Assets/Scripts/Models/CoachResponse.cs

@@ -0,0 +1,16 @@
+using System;
+using Newtonsoft.Json;
+
+namespace CommanderAILab.Models
+{
+    /// <summary>Maps to POST /api/coach/chat response.</summary>
+    [Serializable]
+    public class CoachResponse
+    {
+        [JsonProperty("reply")] public string reply;
+        [JsonProperty("deck_report")] public string deckReport;
+        [JsonProperty("suggestions")] public string[] suggestions;
+
+        public override string ToString() => reply ?? "(empty coach response)";
+    }
+}