style: refine admin & me UI — card forms, back arrows, avatar in admin sidebar, Empty component

- Replace ← text with icon-[ri--arrow-left-line] in admin and me layouts
- Add avatar + admin shield badge to admin sidebar header
- Wrap all admin edit forms in Card (bg-card/50 border-primary/20) with styled inputs
- Fix sm:pl-6 → lg:pl-6 so extra left padding only applies when sidebar is visible
- Update security form submit button to gradient style matching profile
- Remove "View Public Profile" button from me/profile
- Use shadcn-svelte Empty component for recordings empty state
- Install empty component via shadcn-svelte

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

packages/frontend/src/routes/admin/articles/+page.svelte

@@ -67,7 +67,7 @@
 
 <Meta title={$_("admin.articles.title")} description={null} />
 
-<div class="py-3 sm:py-6 sm:pl-6">
+<div class="py-3 sm:py-6 lg:pl-6">
   <div class="flex items-center justify-between mb-6 px-3 sm:px-0">
     <h1 class="text-2xl font-bold">{$_("admin.articles.title")}</h1>
     <div class="flex items-center gap-3">