remove clsx usage

Svelte 5.16 introduced the same syntax for `class` directives: https://svelte.dev/docs/svelte/class#Attributes-Objects-and-arrays

So everywhere we do this:
```svelte
<div class={clsx([...])}></div>
```

change it to this
```svelte
<div class={[...]}></div>
```

And then remove the `clsx` dependency