Some issues around embedded StackBlitz

The StackBlitz's webcontainer doesn't work in Firefox and Safari when it's embedded (iframe).

The full StackBlitz web app (not embedded) does work in Safari and Firefox.

The issue for embedded probably needs to wait for StackBlitz themselves.

Two other issues can be solved:
* [ ] use vite, not webpack with StackBlitz.
* [ ] opened tabs didn't show all files.

For example, first example in playground only shows my-app.html, there is no way to open my-app.ts


Inspect the playground's embedded StackBlitz configuration and reproduce the first example, where only my-app.html is visible and my-app.ts cannot be opened. Check the bundler setup, then verify that the playground uses Vite and that all opened tabs expose their files; Firefox and Safari embedding remains dependent on StackBlitz.

Written by the indexing model from the issue text.