Solution cleanup. Implement stubs for all remaining services. Add API models. Move configuration to appsettings.

src/Models/Entities/EntityIUserPremiumItem.cs

@@ -0,0 +1,14 @@
+using MariesWonderland.Models.Type;
+
+namespace MariesWonderland.Models.Entities;
+
+public class EntityIUserPremiumItem
+{
+    public long UserId { get; set; }
+
+    public int PremiumItemId { get; set; }
+
+    public long AcquisitionDatetime { get; set; }
+
+    public long LatestVersion { get; set; }
+}