feat(tier): Erwerb/Kauf je Tier (Datum, Preis, Notiz)

Co-Authored-By: Claude Opus 4.8 <noreply@anthropic.com>

GerbilManagerWebAPI/Program.cs

@@ -127,6 +127,7 @@ app.MapCmsEndpoints();
 app.MapRequestEndpoints();
 app.MapNamesEndpoints();
 app.MapFeedbackEndpoints();
+app.MapAcquisitionEndpoints();
 
 app.Run();