Move catalog title update validation to handler

Validation preventing CatTitle changes during updates is now enforced in UpdateCatalogHandler instead of the controller. The handler throws an exception if a title change is attempted. Also, streamlined UpdateProcedure handling and removed redundant CatTitle mapping logic.

DbFirst.API/Controllers/CatalogsController.cs

@@ -50,17 +50,6 @@ public class CatalogsController : ControllerBase
     [HttpPut("{id:int}")]
     public async Task<ActionResult<CatalogReadDto>> Update(int id, CatalogWriteDto dto, CancellationToken cancellationToken)
     {
-        var current = await _mediator.Send(new GetCatalogByIdQuery(id), cancellationToken);
-        if (current == null)
-        {
-            return NotFound();
-        }
-        if (dto.UpdateProcedure == CatalogUpdateProcedure.Update &&
-            !string.Equals(current.CatTitle, dto.CatTitle, StringComparison.OrdinalIgnoreCase))
-        {
-            return BadRequest("Titel kann nicht geändert werden.");
-        }
-
         var updated = await _mediator.Send(new UpdateCatalogCommand(id, dto), cancellationToken);
         if (updated == null)
         {