feat: upgrade to PHP 8.0 and modernize codebase}
* Update minimum PHP version requirement to 8.0 in documentation and package.json
* Refactor Tree.php model with improved logic and additional functionality
* Enhance JavaScript index.js with modernized code patterns and better organization
* Reorganize and simplify themes.js for improved maintainability
* Update markdown stylesheet with new styling rules
* Simplify twig template layout by removing unnecessary markup
* Update all changelog entries and documentation references to reflect changes
* Bump application version in Application.php