Publish @docsearch/preact package alongside @docsearch/react

## Describe the problem

Using docsearch directly with Preact currently requires manual configuration.

For example, using `@docsearch/react` in Vite.js projects requires manual fiddling to replace `require("react")` with `require("preact/compat")`.

## Describe the solution

Publish a `@docsearch/preact` package that uses [the same setup as `@docsearch/js`](https://github.com/algolia/docsearch/blob/next/packages/docsearch-js/babel.config.js#L25-L32) to replace react with preact.

`@docsearch/js` could depend on `@docsearch/preact` directly instead.

Start by comparing the existing @docsearch/react package with the @docsearch/js Babel setup linked in the issue, then trace how packages are published and how @docsearch/js declares dependencies. The work is done when a published @docsearch/preact package supports the described Vite.js setup without manual React-to-Preact configuration and the dependency arrangement matches the issue proposal.

Written by the indexing model from the issue text.