refactor(ui): rename route /korrespondenz → /briefwechsel

Update all internal links (AppNav, CoCorrespondentsList, goto) to the
new URL. No redirect needed — no production URLs exist yet.

Refs: #179

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

frontend/src/routes/briefwechsel/SinglePersonHintBar.svelte

@@ -0,0 +1,50 @@
+<script lang="ts">
+import { m } from '$lib/paraglide/messages.js';
+
+interface Props {
+	senderName: string;
+	fromDate?: string;
+	toDate?: string;
+	sortDir?: string;
+}
+
+let { senderName, fromDate = '', toDate = '', sortDir = 'DESC' }: Props = $props();
+
+let hasDateFilter = $derived(!!(fromDate || toDate));
+let sortLabel = $derived(
+	sortDir === 'ASC' ? m.conv_strip_sort_oldest() : m.conv_strip_sort_newest()
+);
+let fromYear = $derived(fromDate ? fromDate.substring(0, 4) : '');
+let toYear = $derived(toDate ? toDate.substring(0, 4) : '');
+</script>
+
+<div
+	class="flex items-center gap-[5px] border-b border-accent bg-accent-bg px-[18px] py-[6px] text-xs text-ink"
+>
+	<svg
+		xmlns="http://www.w3.org/2000/svg"
+		width="14"
+		height="14"
+		viewBox="0 0 24 24"
+		fill="none"
+		stroke="currentColor"
+		stroke-width="1.5"
+		stroke-linecap="round"
+		stroke-linejoin="round"
+		aria-hidden="true"
+		class="shrink-0"
+	>
+		<path d="M9 5H7a2 2 0 0 0-2 2v12a2 2 0 0 0 2 2h10a2 2 0 0 0 2-2V7a2 2 0 0 0-2-2h-2" />
+		<rect x="9" y="3" width="6" height="4" rx="1" />
+	</svg>
+
+	{#if hasDateFilter}
+		<strong>{senderName}</strong>
+		<span>·</span>
+		<span>{fromYear}–{toYear}</span>
+		<span>·</span>
+		<span>{sortLabel}</span>
+	{:else}
+		Alle Briefe von <strong>{senderName}</strong> — wähle einen Korrespondenten oben um einzugrenzen
+	{/if}
+</div>