feat: replace clsx with cn util

src/shared/ui/Button/ButtonGroup.svelte

@@ -4,7 +4,7 @@
     Use for segmented controls, view toggles, or any mutually exclusive button set.
 -->
 <script lang="ts">
-import clsx from 'clsx';
+import { cn } from '$shared/lib';
 import type { Snippet } from 'svelte';
 import type { HTMLAttributes } from 'svelte/elements';
 
@@ -23,7 +23,7 @@ let { children, class: className, ...rest }: Props = $props();
 </script>
 
 <div
-    class={clsx(
+    class={cn(
         'flex items-center gap-1 p-1',
         'bg-surface dark:bg-dark-bg',
         'border border-subtle',