feat(nav): add TabletNavBar with horizontal pills and active state

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

frontend/src/lib/nav/TabletNavBar.svelte

@@ -0,0 +1,22 @@
+<script lang="ts">
+	import { page } from '$app/stores';
+	import { mobileNavItems } from './nav';
+</script>
+
+<nav
+	aria-label="Hauptnavigation"
+	class="hidden md:flex lg:hidden gap-2 items-center p-2"
+>
+	{#each mobileNavItems as item (item.href)}
+		{@const active = $page.url.pathname.startsWith(item.href)}
+		<a
+			href={item.href}
+			aria-current={active ? 'page' : undefined}
+			class="px-4 py-2 rounded-[var(--radius-md)] text-[13px] font-[var(--font-sans)] {active
+				? 'bg-[var(--green-tint)] text-[var(--green-dark)] font-medium'
+				: ''}"
+		>
+			{item.label}
+		</a>
+	{/each}
+</nav>