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/+layout.svelte

@@ -1,8 +1,17 @@
 <script lang="ts">
   import { page } from "$app/state";
   import { _ } from "svelte-i18n";
+  import { Avatar, AvatarImage, AvatarFallback } from "$lib/components/ui/avatar";
+  import { getUserInitials } from "$lib/utils";
+  import { getAssetUrl } from "$lib/api";
 
-  const { children } = $props();
+  const { children, data } = $props();
+
+  const user = $derived(data.authStatus.user!);
+  const avatarUrl = $derived(
+    user.avatar ? (getAssetUrl(user.avatar, "thumbnail") ?? undefined) : undefined,
+  );
+  const displayName = $derived(user.artist_name ?? user.email);
 
   const navLinks = $derived([
     { name: $_("admin.nav.users"), href: "/admin/users", icon: "icon-[ri--team-line]" },
@@ -33,9 +42,10 @@
       <div class="flex items-center gap-1 overflow-x-auto py-2 scrollbar-none">
         <a
           href="/"
-          class="shrink-0 text-xs text-muted-foreground hover:text-foreground transition-colors px-2"
+          class="shrink-0 flex items-center gap-1 text-xs text-muted-foreground hover:text-foreground transition-colors px-2"
         >
-          {$_("admin.nav.back_mobile")}
+          <span class="icon-[ri--arrow-left-line] h-4 w-4"></span>
+          <span class="hidden sm:inline">{$_("admin.nav.back_mobile")}</span>
         </a>
         {#each navLinks as link (link.href)}
           <a
@@ -58,10 +68,27 @@
       <!-- Sidebar (desktop only) -->
       <aside class="hidden lg:flex w-56 shrink-0 flex-col border-r border-border/40">
         <div class="px-4 py-5 border-b border-border/40">
-          <a href="/" class="text-xs text-muted-foreground hover:text-foreground transition-colors">
+          <a href="/" class="flex items-center gap-1 text-xs text-muted-foreground hover:text-foreground transition-colors">
+            <span class="icon-[ri--arrow-left-line] h-3.5 w-3.5"></span>
             {$_("admin.nav.back_to_site")}
           </a>
-          <h1 class="mt-2 text-base font-bold text-foreground">{$_("admin.nav.title")}</h1>
+          <div class="mt-3 flex items-center gap-3">
+            <div class="relative shrink-0">
+              <Avatar class="h-9 w-9">
+                <AvatarImage src={avatarUrl} alt={displayName} />
+                <AvatarFallback class="text-xs">
+                  {getUserInitials(displayName)}
+                </AvatarFallback>
+              </Avatar>
+              <span class="absolute -bottom-1 -right-1 flex h-4 w-4 items-center justify-center rounded-full bg-primary ring-2 ring-background">
+                <span class="icon-[ri--shield-keyhole-fill] h-2.5 w-2.5 text-primary-foreground"></span>
+              </span>
+            </div>
+            <div class="min-w-0">
+              <p class="text-sm font-semibold text-foreground truncate">{displayName}</p>
+              <p class="text-xs text-primary font-medium">{$_("admin.nav.title")}</p>
+            </div>
+          </div>
         </div>
 
         <nav class="flex-1 p-3 space-y-1">