feat: Improve material ordering and default type in MCP tools

- Add SortOrder as secondary ordering key after Shape across all material
  queries (list_materials, search methods)
- Default material type to "Steel" when not specified in add_stock_with_offering

Co-Authored-By: Claude Opus 4.5 <noreply@anthropic.com>

CutList.Web/Controllers/MaterialsController.cs

@@ -22,6 +22,7 @@ public class MaterialsController : ControllerBase
         var materials = await _context.Materials
             .Where(m => m.IsActive)
             .OrderBy(m => m.Shape)
+            .ThenBy(m => m.SortOrder)
             .ThenBy(m => m.Size)
             .Select(m => new MaterialDto
             {