[WIP] Rework the entire plugin to use injectRoute (View Modes now have own route 🎉)

[trueberryless]

Astro features rendering pages at build time even for plugins like this one. By injecting routes at build time, the View Modes can load much faster for the users + WAY less JS is needed to handle the view modes states...

Another benefit of these changes is the separation of the different Zen Mode options, which makes writing the CSS rules a lot cleaner and easier (more beneficial for me instead of end users of course... :))

Things need to be done before merge:

• Switch Buttons must be adapted (less JS because they just link to the /zen-mode route 🎉)
• Navigation has to be intercepted to keep user in same mode
• Footer must be rendered (StarlightPage props problem maybe): See Discord Support Thread
• i18n support must be implemented (could be done in another PR)

[changeset-bot]

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Latest commit: e8ba227

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