Adopt Vite 8

[nedtwigg]

• vite-react-ssg doesn't support Vite 8 yet, but a PR has been merged
• if we drop vite-react-ssg, then we can bump react-router from 6 to 7 and also get Vite 8
  • but not sure if we can get stuff like this to work that way https://dormouse.sh/changelog/after/v0.9.0