test: cover geschichten/new and geschichten/[id]/edit page renders

Both pages embed GeschichteEditor (TipTap-based). The tests assert
heading, BackButton presence, no-error default, editor inputs render,
and prop pass-through (initialPersons / initialDocuments). $app/navigation
is mocked because GeschichteEditor pulls beforeNavigate transitively.

Refs #496.

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

frontend/src/routes/geschichten/[id]/edit/page.svelte.test.ts

@@ -0,0 +1,63 @@
+import { describe, it, expect, vi, afterEach } from 'vitest';
+import { cleanup, render } from 'vitest-browser-svelte';
+import { page } from 'vitest/browser';
+
+vi.mock('$app/navigation', () => ({
+	beforeNavigate: () => {},
+	afterNavigate: () => {},
+	goto: vi.fn(),
+	invalidate: vi.fn(),
+	invalidateAll: vi.fn(),
+	preloadCode: vi.fn(),
+	preloadData: vi.fn(),
+	pushState: vi.fn(),
+	replaceState: vi.fn(),
+	disableScrollHandling: vi.fn(),
+	onNavigate: () => () => {}
+}));
+
+const { default: GeschichtenEditPage } = await import('./+page.svelte');
+
+afterEach(cleanup);
+
+const baseData = (overrides: Record<string, unknown> = {}) => ({
+	geschichte: {
+		id: 'g1',
+		title: 'Die Reise nach Berlin',
+		body: '<p>Im Jahr 1923...</p>',
+		status: 'PUBLISHED' as 'DRAFT' | 'PUBLISHED',
+		persons: [],
+		documents: []
+	},
+	...overrides
+});
+
+describe('geschichten/[id]/edit page', () => {
+	it('renders the geschichte title in the heading', async () => {
+		render(GeschichtenEditPage, { props: { data: baseData() } });
+
+		await expect
+			.element(page.getByRole('heading', { level: 1, name: /reise nach berlin/i }))
+			.toBeVisible();
+	});
+
+	it('renders a button (BackButton component)', async () => {
+		render(GeschichtenEditPage, { props: { data: baseData() } });
+
+		const buttons = document.querySelectorAll('button');
+		expect(buttons.length).toBeGreaterThan(0);
+	});
+
+	it('does not render an error alert by default', async () => {
+		render(GeschichtenEditPage, { props: { data: baseData() } });
+
+		expect(document.querySelector('[role="alert"]')).toBeNull();
+	});
+
+	it('renders the GeschichteEditor with form inputs', async () => {
+		render(GeschichtenEditPage, { props: { data: baseData() } });
+
+		const inputs = document.querySelectorAll('input, textarea, [contenteditable]');
+		expect(inputs.length).toBeGreaterThan(0);
+	});
+});