docs: explain Tailwind styling in v1

[alectimison-maker]

Summary

• document how to replace the v0 classes prop in v1
• add copy-pasteable Tailwind examples for the assembled Select and unstyled primitives
• explain how teleporting affects popover styling

Motivation

The migration guide currently covers the bundled stylesheet and data hooks, but it does not say what replaces the v0 classes prop. This leaves Tailwind users without a clear v1 path.

Testing

• pnpm --filter @vue3-select-component/docs lint
• pnpm --filter @vue3-select-component/docs exec nuxt prepare
• git diff --check

Closes #453

[TotomInc]

Thanks, that closes the documentation gap !