Add project files.

JSMR.Domain/Entities/Series.cs

@@ -0,0 +1,12 @@
+namespace JSMR.Domain.Entities;
+
+public class Series
+{
+    public int SeriesId { get; set; }
+
+    public int CircleId { get; set; }
+    public Circle? Circle { get; set; }
+
+    public required string Name { get; set; }
+    public required string Identifier { get; set; }
+}