fix: update production URL and resolve all build warnings

- Update production URL to devex.intersectmbo.org
- Fix broken footer link: /docs/get-started -> /docs/getting-started
- Disable blog plugin (no blog posts yet)
- Fix all broken markdown links to use correct relative paths
- Update .gitignore to exclude build artifacts and old directories
- Keep strict link checking (onBrokenLinks and onBrokenMarkdownLinks set to 'throw')

Build completes successfully with zero errors/warnings ✅

Fixes #65

Author: “ danbaruka”