Merge feature/litter-mortality (LITTER-MORTALITY-BE): Litter.DeathsWithin8Weeks int? + additive Migration + DTO + Validierung <=TotalBorn

GerbilManagerWebAPI/Models/Litter.cs

@@ -13,6 +13,10 @@ namespace GerbilManagerWebAPI.Models
         /// <summary>Total born count (was "Strength").</summary>
         public int? TotalBorn { get; set; }
 
+        /// <summary>Frühsterblichkeit: Anzahl der in den ersten 8 Wochen verstorbenen Tiere.
+        /// Null = unbekannt (Altdaten). Must be ≤ TotalBorn if both are set.</summary>
+        public int? DeathsWithin8Weeks { get; set; }
+
         public Guid? FatherId { get; set; }
         public Gerbil? Father { get; set; }
         public Guid? MotherId { get; set; }