fix buttons missing type="button"

Triggers unintentional form submits if missing `type` property.

src/lib/StateMachine.svelte

@@ -334,6 +334,7 @@
 	<!-- Back button -->
 	{#if backButtonVisible}
 		<button
+			type="button"
 			class="text-sui-text hover:text-sui-text-700 dark:text-sui-background dark:hover:text-sui-background/80 flex cursor-pointer items-center
 			gap-2.5 font-medium transition-colors"
 			onclick={() => (index -= 1)}