feat(search): add SortDropdown component with direction toggle

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

frontend/src/lib/components/SortDropdown.svelte

@@ -0,0 +1,36 @@
+<script lang="ts">
+import * as m from '$lib/paraglide/messages.js';
+
+interface Props {
+	sort: string;
+	dir: string;
+}
+
+let { sort = $bindable(), dir = $bindable() }: Props = $props();
+
+function toggleDir() {
+	dir = dir === 'asc' ? 'desc' : 'asc';
+}
+</script>
+
+<div class="inline-flex items-center gap-1">
+	<select
+		role="combobox"
+		bind:value={sort}
+		class="border-brand-sand rounded border bg-white px-2 py-1 font-sans text-sm text-brand-navy focus:ring-2 focus:ring-brand-mint focus:outline-none"
+	>
+		<option value="DATE">{m.docs_sort_date()}</option>
+		<option value="TITLE">{m.docs_sort_title()}</option>
+		<option value="SENDER">{m.docs_sort_sender()}</option>
+		<option value="RECEIVER">{m.docs_sort_receiver()}</option>
+		<option value="UPLOAD_DATE">{m.docs_sort_upload()}</option>
+	</select>
+	<button
+		type="button"
+		onclick={toggleDir}
+		class="border-brand-sand hover:bg-brand-sand flex items-center justify-center rounded border bg-white px-2 py-1 text-sm text-brand-navy transition-colors"
+		aria-label={dir === 'asc' ? 'Aufsteigend sortieren' : 'Absteigend sortieren'}
+	>
+		{dir === 'asc' ? '↑' : '↓'}
+	</button>
+</div>