FEAT-14a: Charakterbogen on Gerbil (traits + note) + sale-ad request extension

- Gerbil.CharacterTraits (List<string>, JSON text column, opaque labels) + CharacterNote
  (string?). On GerbilDto + Input; round-trips on GET/POST/PUT. Additive migration.
- SaleAdAnimal gains Traits (German labels) + CharacterNote; prompt builder emits
  "Charakter: …" + "Charakter-Notiz: …" lines for the AI Verkaufstext.
- Tests: traits/note round-trip (POST->GET via SQLite host), empty-default, prompt inclusion.

GerbilManagerWebAPI/Dtos/ApiDtos.cs

@@ -25,7 +25,9 @@ namespace GerbilManagerWebAPI.Dtos
         string? Notes,
         string? ImportSource,
         string? ExternalRef,
-        string? OriginBreeder);
+        string? OriginBreeder,
+        List<string> CharacterTraits,
+        string? CharacterNote);
 
     public record LitterDto(
         Guid Id,
@@ -71,7 +73,9 @@ namespace GerbilManagerWebAPI.Dtos
         string? Notes,
         string? ImportSource,
         string? ExternalRef,
-        string? OriginBreeder);
+        string? OriginBreeder,
+        List<string>? CharacterTraits,
+        string? CharacterNote);
 
     public record LitterInput(
         string Name,