feat(manacore/web): add undo toasts for delete and tag removal

Extend toast system with action buttons and toastStore.undo() helper.
After deleting a task/event/contact or removing a tag, a toast with
"Rückgängig" button appears for 5 seconds. Clicking it restores the
item (clears deletedAt) or re-adds the tag.

Co-Authored-By: Claude Opus 4.6 (1M context) <noreply@anthropic.com>

packages/shared-ui/src/toast/ToastContainer.svelte

@@ -31,6 +31,17 @@
 			<div class="toast-item {colors[toast.type]}" role="alert">
 				<Icon size={20} weight="fill" class="toast-icon" />
 				<p class="toast-message">{toast.message}</p>
+				{#if toast.action}
+					<button
+						onclick={() => {
+							toast.action?.onClick();
+							handleDismiss(toast.id);
+						}}
+						class="toast-action"
+					>
+						{toast.action.label}
+					</button>
+				{/if}
 				<button
 					onclick={() => handleDismiss(toast.id)}
 					class="toast-dismiss"
@@ -92,6 +103,23 @@
 		margin: 0;
 	}
 
+	.toast-action {
+		flex-shrink: 0;
+		padding: 0.25rem 0.625rem;
+		border-radius: 0.375rem;
+		background: rgba(255, 255, 255, 0.2);
+		border: 1px solid rgba(255, 255, 255, 0.3);
+		cursor: pointer;
+		font-size: 0.75rem;
+		font-weight: 600;
+		color: inherit;
+		transition: all 0.15s ease;
+		white-space: nowrap;
+	}
+	.toast-action:hover {
+		background: rgba(255, 255, 255, 0.35);
+	}
+
 	.toast-dismiss {
 		flex-shrink: 0;
 		padding: 0.25rem;

packages/shared-ui/src/toast/index.ts

@@ -1,5 +1,5 @@
 export { toastStore, toast, handleApiError } from './toast.svelte';
-export type { Toast, ToastType } from './toast.svelte';
+export type { Toast, ToastType, ToastAction } from './toast.svelte';
 export { default as ToastContainer } from './ToastContainer.svelte';
 export { setupGlobalErrorHandler, GLOBAL_ERROR_TRANSLATIONS } from './globalErrorHandler';
 export type {

packages/shared-ui/src/toast/toast.svelte.ts

@@ -20,11 +20,17 @@
 
 export type ToastType = 'success' | 'error' | 'warning' | 'info';
 
+export interface ToastAction {
+	label: string;
+	onClick: () => void;
+}
+
 export interface Toast {
 	id: string;
 	type: ToastType;
 	message: string;
 	duration: number;
+	action?: ToastAction;
 }
 
 // State
@@ -50,11 +56,12 @@ export const toastStore = {
 	 * @param message - The message to display
 	 * @param type - Toast type: 'success' | 'error' | 'warning' | 'info'
 	 * @param duration - Duration in ms (0 = permanent, default: 4000)
+	 * @param action - Optional action button { label, onClick }
 	 * @returns The toast ID for manual dismissal
 	 */
-	show(message: string, type: ToastType = 'info', duration = 4000): string {
+	show(message: string, type: ToastType = 'info', duration = 4000, action?: ToastAction): string {
 		const id = generateId();
-		const toast: Toast = { id, type, message, duration };
+		const toast: Toast = { id, type, message, duration, action };
 
 		toasts = [...toasts, toast];
 
@@ -104,6 +111,24 @@ export const toastStore = {
 		return this.show(message, 'info', duration);
 	},
 
+	/**
+	 * Show a success toast with an undo action button.
+	 * @param message - The message to display
+	 * @param onUndo - Callback when "Rückgängig" is clicked
+	 * @param duration - Duration in ms (default: 5000)
+	 */
+	undo(message: string, onUndo: () => void, duration = 5000): string {
+		return this.show(message, 'success', duration, {
+			label: 'Rückgängig',
+			onClick: () => {
+				onUndo();
+				// Find and dismiss this toast after undo
+				const id = toasts.find((t) => t.action?.onClick === onUndo)?.id;
+				if (id) this.dismiss(id);
+			},
+		});
+	},
+
 	/**
 	 * Dismiss a specific toast by ID
 	 * @param id - The toast ID to dismiss