Update to Astro 6, dependencies and fixed any found bugs

[LeandroPata]

Update to Astro 6, dependencies and fixed any found bugs

Summary

This pull request updates astro to astro v6.1.7, as well as all other packages and dependencies.
Also updated all other relevant components and configs due to changes in Astro 6, as well as fixed all bugs found from these changes.

Changes

• Upgraded dependencies and devDependencies in package.json:
  • Astro: 6.1.7;
  • Playwright: 1.59.1;
  • Vitest: 4.1.4;
• Updated theme toggle functionality:
  • Replaced custom JavaScript with native HTML attributes and event listeners;
  • Used localStorage to persist the theme across page reloads;
  • Handled transitions between pages using astro:before-swap and astro:after-swap;
• Refactored tests for theme toggle behavior;
• Updated styles and layout files to reflect changes in class names and structure;
• Updated Github actions to use withastro/action@v6;

Notes

• This update should improve the reliability and performance of the theme toggling feature.
• The new implementation uses native HTML features, which should be more accessible and easier to maintain.