Migrate ReadTheDocs to VitePress engine

[ShutdownRepo]

The Exegol documentation has been migrated from ReadTheDocs (Sphinx with reStructuredText) to VitePress (Markdown-based).

• New engine: Switched to VitePress for improved performance and a modern browsing experience.
• New format: Documentation source files are now in Markdown (.md) instead of reStructuredText (.rst). It lowers the barrier for contributions and simplifies maintenance.
• Enhanced UX/UI: Faster navigation, better styling (more aligned with new graphical chart), better search, and built-in support for features like dark mode.

This change lays the groundwork for more accessible and community-friendly documentation.