[Docs Site] bump dependencies, improve building on Windows

[Cherry]

I was previously getting lots of weird errors when trying to build with Windows, and common solutions involved upgrading Vite.

This PR includes a few maintenance tasks on the docs site:

• I took the time to upgrade Vite and a bunch of other dependencies as much as possible while remaining compatible with Node 20 and each package's current version ranges. I tested this and anecdotally the Vite build feels faster, and I've not been able to find any regressions throughout.
  • Most dep bumps are minor, outside of Vite which is a major version upgrade from 4 -> 5
• Upgrades the volta definition for the Node.js version the latest v20-lts, since that seems to be what's used in CI here now.
• Adds a .gitattributes to better normalise line endings when committing from Windows vs Linux vs Mac, so no mixture of CRLF and LF files

If there's any further testing I can do for this PR here, please let me know.