[docs] Add Previous/Next navigation buttons and Docs links to documentation (AcademySoftwareFoundation#1815)

- Implement page navigation with Previous/Next buttons on all
documentation pages
- Add responsive design and accessibility features for navigation
buttons
- Update nav_order values for all documentation pages to enable
sequential navigation
- Create comprehensive Docs landing page with links to all documentation
sections
- Fix navigation order to match intended documentation hierarchy
- Ensure proper page title display in navigation buttons with fallback
to generic labels
- Remove unused Hugo docs _index.md files (old opencue.io documentation)
- Add new links and icons to View Documents and View documentation
versions

**Link the Issue(s) this Pull Request is related to.**
- AcademySoftwareFoundation#1800

Author: ramonfigueiredo