chore: align NuGet compliance metadata

[janechu]

Summary

• Align shared .NET package metadata with Microsoft NuGet compliance requirements for authorship, ownership metadata, license URL, required license acceptance, release notes, tags, project/repository URLs, and copyright.
• Document the required Microsoft package ownership, Microsoft-certificate package signing, and Authenticode-capable content signing gates before manual nuget.org publishing.
• Add tool-specific NuGet tags while keeping runtime packages on their runtime-specific metadata.

Validation

• cargo xtask check
• Checked nuget.org package IDs; no Microsoft.WebUI NuGet packages are currently published, so there were no existing package signatures to inspect.
• Checked the source checkout for staged NuGet/native artifacts; none were present to signature-check locally.