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/me/security/+page.svelte

@@ -57,13 +57,12 @@
 
 <Meta title={$_("me.settings.privacy_title")} />
 
-<div class="py-3 sm:py-6 sm:pl-6">
-  <div class="flex items-center justify-between mb-6 px-3 sm:px-0">
+<div class="py-3 sm:py-6 lg:pl-6">
+  <div class="flex items-center justify-between mb-6">
     <h1 class="text-2xl font-bold">{$_("me.settings.privacy_title")}</h1>
   </div>
 
-  <div class="px-3 sm:px-0">
-    <Card class="bg-card/50 border-primary/20 max-w-2xl">
+  <Card class="bg-card/50 border-primary/20 max-w-2xl">
       <CardHeader>
         <CardTitle>{$_("me.settings.privacy_title")}</CardTitle>
         <CardDescription>{$_("me.settings.privacy_subtitle")}</CardDescription>
@@ -145,9 +144,8 @@
           {/if}
 
           <Button
-            variant="outline"
             type="submit"
-            class="cursor-pointer w-full border-primary/20 hover:bg-primary/10"
+            class="cursor-pointer w-full bg-gradient-to-r from-primary to-accent hover:from-primary/90 hover:to-accent/90"
             disabled={isSecurityLoading}
           >
             {#if isSecurityLoading}
@@ -162,5 +160,4 @@
         </form>
       </CardContent>
     </Card>
-  </div>
 </div>