docs: add NuGet version badges to root and package READMEs

[Vulthil]

Summary

• Adds a NuGet column to all five package tables in the root README, with a live shields.io version badge per package linking to its nuget.org page.
• Adds the same version badge directly under the title of every package README in src/ (all 24). These READMEs are packed into the packages (PackageReadmeFile), and img.shields.io is on nuget.org's allowed image-domain list, so the badges will also render on each nuget.org package page starting with the next published release (existing package READMEs are immutable).

Badges are served live from img.shields.io/nuget/v/<PackageId>, so they always show the latest stable version with no CI or release-pipeline changes.

The docs-site articles (docs/articles/*.md) intentionally get no badges: the docs site is versioned, and a live latest-version badge inside an older docs snapshot would contradict the version being viewed.

Verification

• git diff is markdown-only: +2 lines per package README (badge + blank line), table rewrite in the root README; CRLF line endings preserved.
• Queried the shields.io endpoint for the published package IDs, including the mixed-case Vulthil.xUnit — both resolve to nuget v1.0.1.

Backport to v1.0: no — cosmetic docs change; servicing releases don't need it, and the badge always shows the latest stable version anyway, which would look out of place on an older package's page.

[claude]

Code review

No issues found. Checked for bugs and CLAUDE.md compliance.