fix(journey-editor): selectedPersons change calls markDirty via $effect

Skip-first-run $effect tracks selectedPersons array length; any add/remove
after mount marks the editor dirty so the unsaved-warning fires on nav.

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

frontend/src/lib/geschichte/JourneyEditor.svelte.spec.ts

@@ -678,6 +678,44 @@ describe('JourneyEditor — unsaved warning banner', () => {
 	});
 });
 
+describe('JourneyEditor — selectedPersons marks dirty', () => {
+	function getNavCallback() {
+		const calls = vi.mocked(beforeNavigate).mock.calls;
+		const [callback] = calls[calls.length - 1];
+		return (cancel = vi.fn()) => {
+			(callback as (nav: { cancel: () => void; to: { url: URL } | null }) => void)({
+				cancel,
+				to: { url: new URL('http://localhost/geschichten') }
+			});
+			return cancel;
+		};
+	}
+
+	it('removing a person chip marks the editor dirty', async () => {
+		render(
+			JourneyEditor,
+			defaultProps({
+				geschichte: makeGeschichte({
+					persons: [{ id: 'p1', firstName: 'Anna', lastName: 'Schmidt' }]
+				})
+			})
+		);
+
+		// Confirm navigation is NOT blocked initially (clean state)
+		const triggerNav = getNavCallback();
+		expect(triggerNav()).not.toHaveBeenCalled();
+
+		// Remove the person chip (aria-label = m.comp_multiselect_remove() = "Entfernen")
+		await userEvent.click(page.getByRole('button', { name: m.comp_multiselect_remove() }));
+
+		// After person removal, navigation should be blocked
+		await vi.waitFor(() => {
+			const cancel = triggerNav();
+			expect(cancel).toHaveBeenCalled();
+		});
+	});
+});
+
 describe('JourneyEditor — person chips from GeschichteView', () => {
 	it('renders person names in the sidebar chips (PersonView carries no displayName)', async () => {
 		render(