Replace `svelte-awesome` with `iconify`

Replace [svelte-awesome](https://github.com/RobBrazier/svelte-awesome) with [iconify](https://github.com/iconify/iconify) ([explore](https://icones.js.org/)) through [unplugin-icons](https://github.com/unplugin/unplugin-icons).
This will provide a wider selection of icons and make them easier to use.