fix(journey-create): catch network rejections and surface error alert

try/finally without catch swallowed TypeError network failures silently.
Added catch block that sets errorMessage so the UI shows role=alert.

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

frontend/src/routes/geschichten/new/JourneyCreate.svelte

@@ -38,6 +38,9 @@ async function handleSubmit(e: SubmitEvent) {
 		}
 		const created = await res.json();
 		goto(`/geschichten/${created.id}/edit`);
+	} catch (e) {
+		console.error('JourneyCreate submit failed', e);
+		errorMessage = getErrorMessage(undefined);
 	} finally {
 		submitting = false;
 	}

frontend/src/routes/geschichten/new/JourneyCreate.svelte.spec.ts

@@ -62,6 +62,22 @@ describe('JourneyCreate — failure path', () => {
 		});
 	});
 
+	it('shows an error alert when the network request rejects (no crash)', async () => {
+		vi.stubGlobal('fetch', vi.fn().mockRejectedValue(new TypeError('network down')));
+		const consoleError = vi.spyOn(console, 'error').mockImplementation(() => {});
+
+		render(JourneyCreate, {});
+
+		await userEvent.fill(
+			page.getByRole('textbox', { name: m.journey_title_aria_label() }),
+			'Meine Lesereise'
+		);
+		await userEvent.click(page.getByRole('button', { name: m.journey_create_submit() }));
+
+		await expect.element(page.getByRole('alert')).toBeInTheDocument();
+		consoleError.mockRestore();
+	});
+
 	it('has an accessible label on the title input', async () => {
 		vi.stubGlobal('fetch', vi.fn());
 		render(JourneyCreate, {});