Add remaining project files

Models/PlayerInvite.cs

@@ -0,0 +1,30 @@
+using LiteDB;
+
+namespace DeluxeBackend.Models
+{
+    public class PlayerInvite
+    {
+        [BsonId]
+        public long Id { get; set; }
+        [BsonRef("accounts")]
+        public required Account Account { get; set; }
+        [BsonRef("accounts")]
+        public required Account InvitedBy { get; set; }
+        public required long InstanceId { get; set; }
+        public required DateTime ExpiresAt { get; set; }
+
+        [BsonIgnore]
+        public bool IsValid
+        {
+            get
+            {
+                var now = DateTime.UtcNow;
+                bool timeValid = ExpiresAt.Kind == DateTimeKind.Utc
+                    ? ExpiresAt > now
+                    : ExpiresAt.ToUniversalTime() > now;
+
+                return timeValid;
+            }
+        }
+    }
+}