Install Nextra

[jv-farias]

Set up Nextra as the documentation and content system for the project, enabling MDX-based pages and built-in theming.

Tasks:

• Install Nextra and required dependencies

• Configure next.config.js to use Nextra as the default theme

• Create initial pages/index.mdx and basic folder structure

• Test that the dev server runs and renders .mdx pages

• Add basic layout and configuration in theme.config.ts

[AbraaoAlves]

The last task could be split for another issue.