Require vike-{react,vue,solid} or add a warning?

[brillout]

I've added a warning telling users to only go for a custom integration (instead of using vike-{react,vue,solid}) if they have a clear reason not to. For example:

• https://vike.dev/new#without-vike-react-vue-solid
• https://vike.dev/solid#manual-integration

Maybe we can also add that warning to Bati. A user scaffolded a Vike app without vike-{react,vue,solid} using Bati and got confused.

Also, I think we can even require vike-{react,vue,solid}, especially if it makes Bati easier to maintain.

[magne4000]

That's a good point, using Bâti without those integrations is mostly pointless anyway.

[magne4000]

Fixed by #390