STATUS-MODEL: Active→Breeding + Pet enum + derived status logic (P0)

GerbilStatus: Active→Breeding, add Pet; Deceased/GivenAway are now DERIVED.
GerbilStatusService.Derive(): central precedence: DateOfDeath→Deceased (1),
ReceiverContactId→GivenAway (2), age>7y→Deceased presumed (3), user choice (4).
All write paths (gerbil CRUD, contracts, importers) call GerbilStatusService.Apply().
Startup sweep flips >7y gerbils to Deceased at next app restart.
Migration StatusModel: Active→Breeding rename + backfill derived statuses.
10 new tests; 200/200 green; has-pending=No.

Enum string values: Breeding (was Active), Pet (new), Deceased, GivenAway, ForSale.
FE contract: status field values updated (see Done-Report).

GerbilManagerWebAPI/Migrations/20260607012436_StatusModel.cs

@@ -0,0 +1,40 @@
+using Microsoft.EntityFrameworkCore.Migrations;
+
+#nullable disable
+
+namespace GerbilManagerWebAPI.Migrations
+{
+    /// <inheritdoc />
+    public partial class StatusModel : Migration
+    {
+        /// <inheritdoc />
+        protected override void Up(MigrationBuilder migrationBuilder)
+        {
+            // 1) Rename string value 'Active' → 'Breeding'.
+            migrationBuilder.Sql(@"UPDATE ""Gerbils"" SET ""Status"" = 'Breeding' WHERE ""Status"" = 'Active';");
+
+            // 2) DateOfDeath set → Deceased (always takes precedence).
+            migrationBuilder.Sql(@"UPDATE ""Gerbils"" SET ""Status"" = 'Deceased' WHERE ""DateOfDeath"" IS NOT NULL;");
+
+            // 3) ReceiverContactId OR SaleContractAnimal → GivenAway (if not already Deceased).
+            migrationBuilder.Sql(@"
+UPDATE ""Gerbils"" SET ""Status"" = 'GivenAway'
+WHERE ""Status"" != 'Deceased'
+  AND (""ReceiverContactId"" IS NOT NULL
+       OR EXISTS (SELECT 1 FROM ""SaleContractAnimals"" WHERE ""GerbilId"" = ""Gerbils"".""Id""));");
+
+            // 4) Age > 7 years (presumed dead) → Deceased, but NOT overriding GivenAway.
+            migrationBuilder.Sql(@"
+UPDATE ""Gerbils"" SET ""Status"" = 'Deceased'
+WHERE ""Status"" NOT IN ('Deceased', 'GivenAway')
+  AND ""DateOfBirth"" IS NOT NULL
+  AND ""DateOfBirth"" < (CURRENT_DATE - INTERVAL '7 years');");
+        }
+
+        /// <inheritdoc />
+        protected override void Down(MigrationBuilder migrationBuilder)
+        {
+            migrationBuilder.Sql(@"UPDATE ""Gerbils"" SET ""Status"" = 'Active' WHERE ""Status"" = 'Breeding';");
+        }
+    }
+}