style: apply gradient to primary buttons in admin area

Co-Authored-By: Claude Sonnet 4.6 <noreply@anthropic.com>

packages/frontend/src/routes/admin/videos/[id]/+page.svelte

@@ -182,7 +182,7 @@
     {/if}
 
     <div class="flex gap-3 pt-2">
-      <Button onclick={handleSubmit} disabled={saving}>
+      <Button onclick={handleSubmit} disabled={saving} class="bg-gradient-to-r from-primary to-accent hover:from-primary/90 hover:to-accent/90">
         {saving ? $_("admin.common.saving") : $_("admin.common.save_changes")}
       </Button>
       <Button variant="outline" href="/admin/videos">{$_("common.cancel")}</Button>