fix(api-dto): import Dto.Shared.projitems so the package actually packs

mass-release.yml stopped on api-dto with NU5026:

  The file '.../Codout.Framework.Api.Dto/bin/Release/netstandard2.1/
  Codout.Framework.Api.Dto.dll' to be packed was not found on disk.

Root cause: Codout.Framework.Api.Dto/ contains only the .csproj — no
.cs files anywhere. The shared types (Dto, IDto, EntityDto<T>,
IEntityDto<T>) live in Codout.Framework.Dto.Shared/ and are pulled
into consumer csprojs via a Shared Project Import. Codout.Framework
.Application and Codout.Framework.Api.Client both do this:

  <Import Project="..\Codout.Framework.Dto.Shared\
                   Codout.Framework.Dto.projitems" Label="Shared" />

Codout.Framework.Api.Dto.csproj never had that line. Build produced
no assembly, and pack had nothing to package.

This fix adds the same Import line. No version bump: the broken 6.3.0
was never produced (pack failed), so the version slot is still free.

https://claude.ai/code/session_015jxScBEvdKkRwGvJTgK5Py

Author: claude

Codout.Framework.Api.Dto/Codout.Framework.Api.Dto.csproj

@@ -14,4 +14,9 @@
     <Folder Include="Default\" />
   </ItemGroup>
 
+  <!-- Same shared-source import pattern used by Codout.Framework.Application and
+       Codout.Framework.Api.Client. Without it this project has zero .cs files,
+       MSBuild produces no assembly, and `dotnet pack` fails with NU5026. -->
+  <Import Project="..\Codout.Framework.Dto.Shared\Codout.Framework.Dto.projitems" Label="Shared" />
+
 </Project>