FEAT-13: SaleContract + BreederSettings entities (additive migration, join table justified in code docs), /contracts + /settings/breeder-profile Minimal-API endpoints w/ Abgabe-completion transaction + SQLite-backed endpoint round-trip tests (21/21)

Co-Authored-By: Claude Opus 4.8 (1M context) <noreply@anthropic.com>

GerbilManagerWebAPI/Dtos/ContractDtos.cs

@@ -0,0 +1,33 @@
+namespace GerbilManagerWebAPI.Dtos
+{
+    // FEAT-13: Abgabeverträge + Zuchtprofil (eigene Datei, hält ApiDtos.cs konfliktfrei).
+
+    public record SaleContractDto(
+        Guid Id,
+        Guid ContactId,
+        decimal Price,
+        DateOnly HandoverDate,
+        DateOnly ContractDate,
+        string FileName,
+        DateTimeOffset CreatedAt,
+        IReadOnlyList<Guid> GerbilIds,
+        // Download-URL der .docx ("/contracts/{id}/file").
+        string Url);
+
+    public record SaleContractInput(
+        Guid ContactId,
+        List<Guid> GerbilIds,
+        decimal Price,
+        DateOnly HandoverDate,
+        DateOnly? ContractDate);
+
+    /// <summary>Zuchtprofil — Antwort UND Request-Body von /settings/breeder-profile.</summary>
+    public record BreederProfileDto(
+        string ZuchtName,
+        string Name,
+        string Address,
+        string Phone,
+        string Email,
+        string Homepage,
+        string City);
+}