refactor: remove unneeded .stackblitzrc, update template dependencies

This PR harmonizes what basic config files we find in a starter template.

What's in `package.json`

Almost all starters have a package.json file. I've tried to harmonize those files to follow this pattern:

{
  "name": "{folder-name}-demo",
  "version": "0.0.0",
  "private": true,
  "scripts": { … },
  "dependencies": { … },
  "devDependencies": { … }
}

Some templates may not have "scripts" (most for some EngineBlock starters), some may not have "devDependencies".

Open questions:

What should we use for the package name?
- Should we include one at all?
- Is the "{folder-name}-demo" pattern okay, or do we want to use “starter” or “template” instead of “demo” maybe?
- Note that if we end up using a name that matches an existing package on npm, running npm info will show information for that package merged with info from the local package.json, which is quite strange, but maybe a very rare problem.
Is the "version" even useful? I’m tempted to just drop it.

Removing all the `.stackblitzrc` files

All the .stackblitzrc files in WebContainer projects were spelling out defaults, such as { "installDependencies": true, startCommand: "npm run dev" }.

I removed them for the sake of readability, but if we want to include one with defaults in every WC starter template we could do that too.

Making sure every WC template has a `.gitignore`

For every WebContainer-based template, I made sure it had a .gitignore file that listed at least:

node_modules
whatever caching folder the framework is using (.next, .nuxt, .svelte-kit, etc.)
whatever build output folder resulted from running npm run build (build, dist, etc.)

Harmonizing `index.html` files

Made sure every one had a <!DOCTYPE html>
Removed <meta http-equiv="X-UA-Compatible" content="IE=edge">
Used the same minimal viewport meta everywhere: <meta name="viewport" content="width=device-width">

Harmonizing base CSS styles

We had base style.css files which looked like:

h1, h2 {
  font-family: Lato;
}

That's not super useful, especially since the preview documents don't load the Lato fonts at all. (They used to, in EngineBlock projects, but we removed those fonts in early 2022 for performance reasons.)

Instead I'm proposing a very basic stylesheet looking like this:

* {
  box-sizing: border-box;
}

body {
  margin: 0;
  padding: 1rem;
  font-family: system-ui, sans-serif;
  color: black;
  background-color: white;
}

h1 {
  font-weight: 800;
  font-size: 1.5rem;
}

stackblitz / starters