Replace Hugo+Docsy with Zensical (MkDocs Material). Restructure all
content under docs/ with explicit nav. Add 19 new Go package pages,
plus Agent, MCP, CoreTS, IDE, GUI, and AI (LEM) sections. PHP sidebar
restructured with collapsible Guides/Reference groups. Homepage now
has sidebar with Where to Start guide and Community links.
Tabs: Home | Go | PHP | TS | GUI | AI | Tools | Deploy | Publish
Co-Authored-By: Virgil <virgil@lethean.io>
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