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/+page.server.ts

@@ -0,0 +1,82 @@
+import { error } from '@sveltejs/kit';
+import type { components } from '$lib/generated/api';
+import { createApiClient } from '$lib/api.server';
+import { getErrorMessage } from '$lib/errors';
+
+export async function load({ url, fetch, locals }) {
+	const senderId = url.searchParams.get('senderId') || '';
+	const receiverId = url.searchParams.get('receiverId') || '';
+	const from = url.searchParams.get('from') || '';
+	const to = url.searchParams.get('to') || '';
+	const dir = url.searchParams.get('dir') || 'DESC';
+
+	const canWrite =
+		(locals.user as { groups?: { permissions: string[] }[] } | undefined)?.groups?.some((g) =>
+			g.permissions.includes('WRITE_ALL')
+		) ?? false;
+
+	const api = createApiClient(fetch);
+
+	let documents: components['schemas']['Document'][] = [];
+	let senderName = '';
+	let receiverName = '';
+
+	const requests: Promise<void>[] = [];
+
+	if (senderId) {
+		requests.push(
+			api
+				.GET('/api/documents/conversation', {
+					params: {
+						query: {
+							senderId,
+							receiverId: receiverId || undefined,
+							dir,
+							from: from || undefined,
+							to: to || undefined
+						}
+					}
+				})
+				.then((result) => {
+					if (!result.response.ok) {
+						const code = (result.error as unknown as { code?: string })?.code;
+						throw error(result.response.status, getErrorMessage(code));
+					}
+					documents = result.data ?? [];
+				})
+		);
+
+		requests.push(
+			api.GET('/api/persons/{id}', { params: { path: { id: senderId } } }).then((result) => {
+				if (!result.response.ok) {
+					const code = (result.error as unknown as { code?: string })?.code;
+					throw error(result.response.status, getErrorMessage(code));
+				}
+				const p = result.data as { firstName: string; lastName: string } | undefined;
+				if (p) senderName = `${p.firstName} ${p.lastName}`;
+			})
+		);
+	}
+
+	if (receiverId) {
+		requests.push(
+			api.GET('/api/persons/{id}', { params: { path: { id: receiverId } } }).then((result) => {
+				if (!result.response.ok) {
+					const code = (result.error as unknown as { code?: string })?.code;
+					throw error(result.response.status, getErrorMessage(code));
+				}
+				const p = result.data as { firstName: string; lastName: string } | undefined;
+				if (p) receiverName = `${p.firstName} ${p.lastName}`;
+			})
+		);
+	}
+
+	await Promise.all(requests);
+
+	return {
+		documents,
+		canWrite,
+		initialValues: { senderName, receiverName },
+		filters: { senderId, receiverId, from, to, dir }
+	};
+}