chore(deps): migrate to astro v5

[hendriknielaender]

Current bugs:

• [category]/[...page].astro:48:21 - undefined is not an object (evaluating 'page.currentPage')

[hendriknielaender]

@flyck when you have time, would be cool if we move to v5 :)

Some little bugs needs to be fixed before we can move here.

[flyck]

Noticed a few things:

• release post mentions an official image component. Tried to switch but that doesnt support the aspectRatio which we need. Would need a deeper look so we can switch
• We have some unused code like the inbuild splitbee analytics or the post categories functionality which we don't use. I guess we dont need the categories, right?
• Upstream repo has some more goodies which could improve the codebase and could be worth a look.

Other than that this works locally, I visited all major pages and checked also for console errors. 👍🏻

[flyck]

Instead of using as Post[] we can also switch to the upstream typescript utils. These have kind of a big diff though, so I would do this another day

https://github.com/onwidget/astrowind/blob/bbcbde87c92a631073e812bd672209effc49abc9/src/utils/blog.ts

[flyck]

Adapting the types is not trivial for an evening job lul. Created a seperate PR: #527