docs: technical integrity audit and alignment with v0.4.0-rc4

[PythonWoods-Dev]

Summary

This PR performs a critical technical audit of the documentation to ensure alignment with the actual codebase and pyproject.toml logic for v0.4.0-rc4.

Key Technical Corrections

• Extras De-mystification: Removed the incorrect claim that zenzic[docs] is required for MkDocs validation. Clarified that Zenzic's MkDocsAdapter is dependency-free and uses a permissive YAML loader to ignore unknown tags natively.
• Installation vs. Execution: Refined the distinction between uvx (ephemeral/CI execution) and uv add --dev (development dependency).
• Static Analysis Limits: Added a new "Static Analysis Limits" section to guide/engines.md. This honestly documents how Zenzic handles !ENV tags (as null), dynamic navigation plugins (ignored), and macros (not evaluated), providing the excluded_dirs workaround.
• Flag Accuracy: Updated the --strict flag description to include its role in triggering external URL validation in addition to treating warnings as errors.
• i18n Parity: All technical corrections have been mirrored in the Italian documentation (docs/it/).

Impact

This update moves Zenzic away from "marketing-driven" documentation toward "engineering-driven" transparency, reducing user friction and preventing unnecessary dependency bloat in user environments.