add FoxchatError type

Foxchat.Core/Models/ApiError.cs

@@ -0,0 +1,17 @@
+namespace Foxchat.Core.Models;
+
+public record ApiError(int Status, ErrorCode Code, string Message);
+
+public enum ErrorCode
+{
+    INTERNAL_SERVER_ERROR,
+    OBJECT_NOT_FOUND,
+    INVALID_SERVER,
+    INVALID_HEADER,
+    INVALID_DATE,
+    INVALID_SIGNATURE,
+    MISSING_SIGNATURE,
+    GUILD_NOT_FOUND,
+    UNAUTHORIZED,
+    INVALID_REST_EVENT,
+}