Refactored AgeGroupController, AgeGroupService, and IAgeGroupService to use string IDs instead of int. Added initial Entity Framework migration and database files to support AltersGruppe with string primary key.
Changed AltersGruppe model ID from int to string and now generates ULID automatically. Added AltersGruppeConfiguration for EF Core mapping. Updated ApplicationDbContext to apply configurations from assembly. Removed obsolete migration files and database artifacts. Added Ulid package dependency.
