Move ApiResult<T> to ApiResult.cs with proper namespace

ApiResult<T> and its static methods were relocated from CatalogApiClient.cs to a new ApiResult.cs file. The new file now includes the DbFirst.BlazorWebApp.Models namespace for better code organization.

DbFirst.BlazorWebApp/Services/CatalogApiClient.cs

@@ -61,11 +61,4 @@ public class CatalogApiClient
         var error = await ApiClientHelper.ReadErrorAsync(response);
         return ApiResult<bool>.Fail(error);
     }
-}
-
-public record ApiResult<T>(bool Success, T? Value, string? Error)
-{
-    public static ApiResult<T> Ok(T? value) => new(true, value, null);
-    public static ApiResult<T> Fail(string? error) => new(false, default, error);
-}
-
+}