Next.js 15.5 + Some minor bumps

[AdrianAndersen]

• chore: bump most deps, update eslint config
  I replaced eslint-plugin-import with eslint-plugin-import-x, which is the new cool kid on the block, which addresses a few issues eslint-plugin-import refuses to address

• chore: bump Next.js to 15.5

I upgraded to Next.js 15 using the instructions in the biog post. Please note the two following things:

1. I enabled type safe routing 🎉 , but then immediately ignored a couple of cases where it flagged something as unsafe. I guess we will fix those in the future ™️ 🤠
2. Turbopack for production builds are now in beta, but we must wait for Serwist to be compatible before we enable it (I think they will add support for it in Serwist 10)