Add View Transitions for smoother page navigation

[antoinekm]

Description
Currently, the website uses traditional full-page refreshes for navigation between pages, causing flickering and a less fluid user experience. This also causes state to be lost between page navigations and can make the site feel slower than it actually is.
We should implement Astro's built-in View Transitions API to create a Single-Page Application (SPA) style navigation experience without requiring a full JavaScript framework. This would:

• Create smoother transitions between pages
• Maintain state between navigations
• Improve perceived performance
• Provide a more modern, app-like feel

Astro has first-class support for view transitions, and we can implement this with minimal changes to our codebase by adding the <ClientRouter /> component to our root layout.