Pin one Zensical version for framework and documentation builds #527

Problem

The Process-PSModule documentation workflow and Install-Zensical action install an unpinned zensical package. MSXOrg/docs pins zensical==0.0.57, so local, documentation, and generated-module builds can currently resolve different releases and produce different behavior.

Expected outcome

Process-PSModule declares one reviewed Zensical version and uses it consistently for its own documentation build and generated module sites.

Acceptance criteria

• Declare one exact Zensical version in a single maintained dependency source.
• Make .github/workflows/Docs.yml and .github/actions/Install-Zensical consume that version without duplicating it.
• Validate Process-PSModule's hand-authored site and a staged Template-PSModule generated site with the pinned version.
• Document the update path for future Zensical releases.
• Keep the pin aligned with MSXOrg/docs unless a documented framework compatibility exception requires otherwise.

References

• MSXOrg/docs requirements.txt
• 🚀 [Feature]: Module repositories share one auditable baseline #525
• 🪲 [Fix]: New modules inherit the current repository baseline Template-PSModule#53