Laser focus hosted docs on being a Noir backend

[johnathan79717]

Problem

The hosted documentation should be laser-focused on barretenberg's role as a Noir backend. Advanced/internal documentation can live elsewhere.

Proposed Changes

Hosted Docs

• Focus exclusively on Noir backend use cases
• Clear, user-friendly guides for common workflows
• Minimal clutter from advanced/internal features

Move to GitHub

• Everything else can be hosted as .md files directly on GitHub
• Internal documentation
• Advanced use-case documentation
• Aztec-specific documentation

Doxygen

• Doxygen can be hosted somewhere (not prominently featured)
• Most end-users don't need to see API reference documentation upfront

Expected Outcome

The hosted docs site should feel purpose-built for Noir users, with a clear learning path and minimal distractions. Power users and contributors can still access advanced documentation through GitHub.