fix(generator): fix NuGet package to include generator DLL

[j-d-ha]

Summary

Fixes critical packaging issue where the source generator DLL was not being included in the NuGet package, causing the generator to not run when consumed from NuGet.org.

Changes

Fixed Generator Packaging

• Changed from @(IntermediateAssembly) to $(OutputPath)\$(AssemblyName).dll in the pack configuration
• The @(IntermediateAssembly) approach doesn't work reliably during the pack phase
• Now the generator DLL is correctly placed in analyzers/dotnet/cs/ folder in the NuGet package

Impact

• Before: Package contained only metadata (icon, README, .nuspec) - generator didn't run
• After: Package contains the generator DLL in the correct location - generator executes and emits source files

Checklist

• The build passes
• Tests have been added or updated (if applicable)
• Documentation has been updated (if applicable)
• Code follows project conventions
• Changes have been tested locally

Related Issues/PRs

Related to PR #7 - this fixes the packaging configuration that was added in that PR.

Reviewer Notes

Verification Steps:

1. Run task pack to build the NuGet package
2. Check package contents: unzip -l ./nupkg/LayeredCraft.SourceGeneratorTools.Generator.0.1.0-alpha.nupkg
3. Verify analyzers/dotnet/cs/LayeredCraft.SourceGeneratorTools.Generator.dll exists in the package (37KB)
4. Test by publishing and consuming from another project

Root Cause:
The @(IntermediateAssembly) MSBuild item doesn't resolve properly during the pack phase, resulting in an empty <None> include that silently fails.

Fix:
Using $(OutputPath)\$(AssemblyName).dll directly references the built DLL from the output directory, which works correctly during pack.