The WriteProtoFileTask now receives RootNamespace and AssemblyName from
MSBuild and uses them for the placeholder proto's csharp_namespace instead
of hardcoded "Generated.Grpc". This ensures GrpcGenerator can find the
service base types on first build, enabling gRPC service registration
to work without requiring a second build.
Co-Authored-By: Claude Opus 4.5 <noreply@anthropic.com>