test(korrespondenz): add Playwright E2E happy-path journey

Cover: empty state loads with search heading, nav link goes to /korrespondenz,
single-person mode shows hint bar, sort toggle updates dir param, bilateral mode
skips gracefully when no co-correspondents exist, swap button reflects swapped IDs
in URL.

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

frontend/e2e/korrespondenz.spec.ts

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+import { test, expect } from '@playwright/test';
+
+test.describe('Korrespondenz – empty state', () => {
+	test('shows the search heading when no person is selected', async ({ page }) => {
+		await page.goto('/korrespondenz');
+		await expect(page.getByText(/Korrespondenz durchsuchen/i)).toBeVisible();
+		await page.screenshot({ path: 'test-results/e2e/korrespondenz-empty.png' });
+	});
+
+	test('nav link goes to /korrespondenz', async ({ page }) => {
+		await page.goto('/');
+		// Click the nav link (desktop text or mobile icon)
+		const navLink = page.getByRole('link', { name: /Korrespondenz/i }).first();
+		await navLink.click();
+		await expect(page).toHaveURL(/\/korrespondenz/);
+	});
+});
+
+test.describe('Korrespondenz – single-person mode', () => {
+	test('shows hint bar and documents when navigated with senderId', async ({ page }) => {
+		// Get a real person ID from the persons list
+		await page.goto('/persons');
+		const firstPersonLink = page.locator('a[href^="/persons/"]').first();
+		await firstPersonLink.click();
+		await page.waitForURL(/\/persons\/.+/);
+
+		// Extract the person ID from the URL
+		const personId = page.url().split('/persons/')[1].split('?')[0];
+
+		// Navigate to korrespondenz in single-person mode
+		await page.goto(`/korrespondenz?senderId=${personId}`);
+
+		// Hint bar should be visible
+		await expect(page.getByText(/Alle Briefe von/i)).toBeVisible();
+
+		// Filter controls should be active (not dimmed)
+		const filterStrip = page.locator('[aria-disabled="false"]').first();
+		await expect(filterStrip).toBeAttached();
+
+		await page.screenshot({ path: 'test-results/e2e/korrespondenz-single-person.png' });
+	});
+
+	test('sort toggle changes URL direction param', async ({ page }) => {
+		await page.goto('/persons');
+		const firstPersonLink = page.locator('a[href^="/persons/"]').first();
+		await firstPersonLink.click();
+		await page.waitForURL(/\/persons\/.+/);
+		const personId = page.url().split('/persons/')[1].split('?')[0];
+
+		await page.goto(`/korrespondenz?senderId=${personId}&dir=DESC`);
+		await page.getByTestId('conv-sort-btn').click();
+
+		await expect(page).toHaveURL(/dir=ASC/);
+		await page.screenshot({ path: 'test-results/e2e/korrespondenz-sort-asc.png' });
+	});
+});
+
+test.describe('Korrespondenz – bilateral mode', () => {
+	test('shows asymmetry bar when both persons have shared documents', async ({ page }) => {
+		// Navigate to a person then follow a co-correspondent suggestion if available
+		await page.goto('/persons');
+		const firstPersonLink = page.locator('a[href^="/persons/"]').first();
+		await firstPersonLink.click();
+		await page.waitForURL(/\/persons\/.+/);
+		const senderId = page.url().split('/persons/')[1].split('?')[0];
+
+		// Try to find a co-correspondent link from the person detail page
+		const corrLink = page
+			.locator('a[href*="/korrespondenz?senderId="][href*="receiverId="]')
+			.first();
+		if (await corrLink.isVisible({ timeout: 2000 }).catch(() => false)) {
+			await corrLink.click();
+			await page.waitForURL(/\/korrespondenz\?.*receiverId=/);
+
+			// Hint bar should NOT be shown in bilateral mode
+			await expect(page.getByText(/Alle Briefe von/i)).not.toBeVisible();
+
+			await page.screenshot({ path: 'test-results/e2e/korrespondenz-bilateral.png' });
+		} else {
+			// No bilateral data available for this person — skip with a note
+			test.skip(true, `No bilateral correspondent links found for person ${senderId}`);
+		}
+	});
+
+	test('swap button swaps sender and receiver in URL', async ({ page }) => {
+		await page.goto('/persons');
+		const firstPersonLink = page.locator('a[href^="/persons/"]').first();
+		await firstPersonLink.click();
+		await page.waitForURL(/\/persons\/.+/);
+		const senderId = page.url().split('/persons/')[1].split('?')[0];
+
+		const corrLink = page
+			.locator('a[href*="/korrespondenz?senderId="][href*="receiverId="]')
+			.first();
+		if (await corrLink.isVisible({ timeout: 2000 }).catch(() => false)) {
+			const href = await corrLink.getAttribute('href');
+			await corrLink.click();
+			await page.waitForURL(/\/korrespondenz\?.*receiverId=/);
+
+			// Extract original receiverId from the href
+			const url = new URL(href!, 'http://x');
+			const originalReceiverId = url.searchParams.get('receiverId')!;
+
+			// Click swap
+			await page.getByTestId('conv-swap-btn').click();
+
+			// After swap the former receiver is now senderId
+			await expect(page).toHaveURL(new RegExp(`senderId=${originalReceiverId}`));
+			await page.screenshot({ path: 'test-results/e2e/korrespondenz-swapped.png' });
+		} else {
+			test.skip(true, `No bilateral correspondent links found for person ${senderId}`);
+		}
+	});
+});