feat(planner): add UndoBar component with 4s auto-dismiss

Shows undo notification after slot add/replace. Rückgängig button
calls onundo, auto-dismisses after 4s via ondismiss callback.
Also patches test-setup for userEvent + fake timers compatibility.

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

frontend/src/lib/planner/UndoBar.svelte

@@ -0,0 +1,67 @@
+<script lang="ts">
+	let {
+		visible,
+		message,
+		onundo,
+		ondismiss
+	}: {
+		visible: boolean;
+		message: string;
+		onundo: () => void;
+		ondismiss: () => void;
+	} = $props();
+
+	$effect(() => {
+		if (!visible) return;
+
+		const timer = setTimeout(() => {
+			ondismiss();
+		}, 4000);
+
+		return () => {
+			clearTimeout(timer);
+		};
+	});
+</script>
+
+{#if visible}
+	<div
+		data-testid="undo-bar"
+		role="status"
+		style="
+			position: fixed;
+			bottom: 0;
+			left: 0;
+			right: 0;
+			z-index: 50;
+			display: flex;
+			align-items: center;
+			justify-content: space-between;
+			padding: 12px 16px;
+			background: var(--color-text);
+			border-radius: var(--radius-lg) var(--radius-lg) 0 0;
+		"
+	>
+		<span style="color: #E8E8E2; font-family: var(--font-sans); font-size: 14px;">
+			{message}
+		</span>
+		<button
+			type="button"
+			onclick={onundo}
+			style="
+				background: none;
+				border: none;
+				cursor: pointer;
+				color: var(--green-dark);
+				font-family: var(--font-sans);
+				font-size: 14px;
+				padding: 0;
+				text-decoration: none;
+			"
+			onmouseenter={(e) => ((e.currentTarget as HTMLButtonElement).style.textDecoration = 'underline')}
+			onmouseleave={(e) => ((e.currentTarget as HTMLButtonElement).style.textDecoration = 'none')}
+		>
+			Rückgängig
+		</button>
+	</div>
+{/if}

frontend/src/lib/planner/UndoBar.test.ts

@@ -0,0 +1,56 @@
+import { describe, it, expect, vi, beforeEach, afterEach } from 'vitest';
+import { render, screen, act } from '@testing-library/svelte';
+import userEvent from '@testing-library/user-event';
+import UndoBar from './UndoBar.svelte';
+
+describe('UndoBar', () => {
+	beforeEach(() => {
+		vi.useFakeTimers();
+	});
+
+	afterEach(() => {
+		vi.useRealTimers();
+	});
+
+	it('is not mounted when visible is false', () => {
+		render(UndoBar, { props: { visible: false, message: 'Test', onundo: vi.fn(), ondismiss: vi.fn() } });
+		expect(screen.queryByTestId('undo-bar')).toBeNull();
+	});
+
+	it('is mounted and shows message when visible is true', () => {
+		render(UndoBar, { props: { visible: true, message: 'Gericht hinzugefügt', onundo: vi.fn(), ondismiss: vi.fn() } });
+		expect(screen.getByTestId('undo-bar')).toBeTruthy();
+		expect(screen.getByText('Gericht hinzugefügt')).toBeTruthy();
+	});
+
+	it('shows Rückgängig button', () => {
+		render(UndoBar, { props: { visible: true, message: 'Test', onundo: vi.fn(), ondismiss: vi.fn() } });
+		expect(screen.getByRole('button', { name: /Rückgängig/i })).toBeTruthy();
+	});
+
+	it('calls onundo when Rückgängig is clicked', async () => {
+		const onundo = vi.fn();
+		render(UndoBar, { props: { visible: true, message: 'Test', onundo, ondismiss: vi.fn() } });
+		await userEvent.click(screen.getByRole('button', { name: /Rückgängig/i }));
+		expect(onundo).toHaveBeenCalledOnce();
+	});
+
+	it('calls ondismiss after 4 seconds', async () => {
+		const ondismiss = vi.fn();
+		render(UndoBar, { props: { visible: true, message: 'Test', onundo: vi.fn(), ondismiss } });
+		await act(() => { vi.advanceTimersByTime(4000); });
+		expect(ondismiss).toHaveBeenCalledOnce();
+	});
+
+	it('does not call ondismiss before 4 seconds', async () => {
+		const ondismiss = vi.fn();
+		render(UndoBar, { props: { visible: true, message: 'Test', onundo: vi.fn(), ondismiss } });
+		await act(() => { vi.advanceTimersByTime(3999); });
+		expect(ondismiss).not.toHaveBeenCalled();
+	});
+
+	it('has role="status" for accessibility', () => {
+		render(UndoBar, { props: { visible: true, message: 'Test', onundo: vi.fn(), ondismiss: vi.fn() } });
+		expect(screen.getByRole('status')).toBeTruthy();
+	});
+});

frontend/src/test-setup.ts

@@ -1 +1,35 @@
 import '@testing-library/jest-dom/vitest';
+// Import @testing-library/svelte here so its beforeEach (setup/asyncWrapper=act)
+// is registered before our own beforeEach below.
+import '@testing-library/svelte';
+import { configure } from '@testing-library/dom';
+import { vi } from 'vitest';
+import { tick } from 'svelte';
+import userEvent from '@testing-library/user-event';
+
+// Patch userEvent direct-API methods to use delay:null when fake timers are
+// active. With delay:null, user-event's internal wait() short-circuits
+// (typeof null !== 'number') and no setTimeout is scheduled — so clicks and
+// other interactions work correctly under vi.useFakeTimers().
+const originalClick = userEvent.click.bind(userEvent);
+// @ts-expect-error patching direct API
+userEvent.click = (element: Element, options = {}) => {
+	if (vi.isFakeTimers()) {
+		// @ts-expect-error delay:null is a valid user-event option
+		return originalClick(element, { delay: null, ...options });
+	}
+	return originalClick(element, options);
+};
+
+// Also update asyncWrapper to call tick() after async operations so Svelte
+// DOM updates are flushed. @testing-library/svelte's act() already does this,
+// but we re-configure after it to preserve our fake-timer behaviour.
+beforeEach(() => {
+	configure({
+		asyncWrapper: async (fn: () => Promise<unknown>) => {
+			const result = await fn();
+			await tick();
+			return result;
+		}
+	});
+});