feat: role-aware nav icons across feed, host, and admin pages

Feed: shows star icon (→ /host) for host/admin, shield icon (→ /admin)
for admin only, alongside the existing account icon.
Host: shows shield icon (→ /admin) for admin only next to "Zur Galerie".
Admin: replaces "Host-Dashboard" text link with star icon (→ /host).

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

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

@@ -158,7 +158,11 @@
 		<div class="mx-auto flex max-w-3xl items-center justify-between px-4 py-4">
 			<h1 class="text-xl font-bold text-gray-900">Admin Dashboard</h1>
 			<div class="flex items-center gap-3">
-				<a href="/host" class="text-sm text-blue-600 hover:underline">Host-Dashboard</a>
+				<a href="/host" class="text-gray-400 hover:text-gray-600" aria-label="Host Dashboard">
+					<svg xmlns="http://www.w3.org/2000/svg" class="h-6 w-6" fill="none" viewBox="0 0 24 24" stroke="currentColor" stroke-width="1.5">
+						<path stroke-linecap="round" stroke-linejoin="round" d="M11.48 3.499a.562.562 0 0 1 1.04 0l2.125 5.111a.563.563 0 0 0 .475.345l5.518.442c.499.04.701.663.321.988l-4.204 3.602a.563.563 0 0 0-.182.557l1.285 5.385a.562.562 0 0 1-.84.61l-4.725-2.885a.562.562 0 0 0-.586 0L6.982 20.54a.562.562 0 0 1-.84-.61l1.285-5.386a.562.562 0 0 0-.182-.557l-4.204-3.602a.562.562 0 0 1 .321-.988l5.518-.442a.563.563 0 0 0 .475-.345L11.48 3.5Z" />
+					</svg>
+				</a>
 				<a href="/feed" class="text-sm text-gray-500 hover:text-gray-700">Galerie</a>
 			</div>
 		</div>