ci: validate docs package version against module manifest

[2chevskii]

Summary

Documentation builds could succeed with a package.json version that differs from the PowerShell module version. Validate package.json's version against ModuleVersion before building documentation in CI and the publishing workflow, and document the requirement to keep them in sync.

Validation

• Pester tests
• Documentation build, when documentation changed
• Manual verification, when applicable

npm run docs:build passed. Executed the validation blocks from both workflows against the repository and isolated fixtures: matching versions pass; mismatched versions, a missing version, and invalid JSON fail. git diff --check passed. Actionlint passed with the existing unknown ubuntu-26.04 runner-label warning excluded. Pester was not run because module behavior is unchanged.

Checklist

• The change is focused and does not include unrelated modifications.
• Tests and documentation have been updated where needed.
• I have read and agree to follow the Code of Conduct.