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/Models/Gerbil.cs

@@ -60,6 +60,13 @@ namespace GerbilManagerWebAPI.Models
         /// Kept in sync automatically on save (see ApplicationContext.SaveChanges). Gridify-filterable
         /// so "clan kleine chaoten" matches "Clan-Kleine-Chaoten" (client strips separators too).</summary>
         public string? NameSearch { get; set; }
+
+        /// <summary>FEAT-14: Charakterbogen trait labels (opaque to the backend — the
+        /// {key,label} vocabulary lives frontend-side). Stored as a JSON text column.</summary>
+        public List<string> CharacterTraits { get; set; } = new();
+
+        /// <summary>FEAT-14: free-text character note; feeds the AI Verkaufstext.</summary>
+        public string? CharacterNote { get; set; }
     }
 
     /// <summary>Shared normalisation for the separator-insensitive name search.</summary>