[Embeds] Create vite project and add to build pipeline (#3448)

* add bskyembed vite app

* create build script (temp until embedr is ready)

bskyembed/src/main.tsx

@@ -0,0 +1,9 @@
+import './index.css'
+
+import {h, render} from 'preact'
+
+import {App} from './app'
+
+const root = document.getElementById('app')
+if (!root) throw new Error('No root element')
+render(<App />, root)