`npx create-stylex-app`

We want to add a `create-stylex-app` (or similar name) scaffolding command that bootstraps a new StyleX project from our existing example templates. We may want to extend this to adding to existing apps as a follow up.

As a sketch:

```
$ npx create-stylex-app [options]

--template: Select a framework or build tool (vite, nextjs, etc.)
--with-reset: Include a reset or starter CSS file
--with-theme: Include a basic theming setup
--strict: Enable stricter defaults and recommended linting
```