fix(ux): replace native confirm() dialogs, add undo-toast, fix prefers-reduced-motion

- Replace all 13 native confirm() calls with confirmModal() across 7 page modules
- Add confirmModal() to modal.js (Promise-based, danger variant, focus management)
- Fix double-confirm bug in contacts.js and budget.js (modal + deleteContact/deleteEntry)
- Extend showToast() with onUndo callback and max-3-toast limit
- Implement optimistic undo-toast (4s window) for shopping item and bulk-checked delete
- Add prefers-reduced-motion guard to btnSuccess() and btnError() in modal.js
- Add btn--error-static CSS class as motion-reduced fallback for btnError()
- Add toast__undo button styles to layout.css
- Add common.confirm and common.undo i18n keys (de, en, it, sv)
- Add shopping.itemDeletedToast i18n key (de, en, it, sv)

public/router.js

@@ -397,10 +397,14 @@ const TOAST_ICONS = {
   warning: '<svg class="toast__icon" viewBox="0 0 24 24" fill="none" stroke="currentColor" stroke-width="2.5" aria-hidden="true"><path d="M10.29 3.86L1.82 18a2 2 0 001.71 3h16.94a2 2 0 001.71-3L13.71 3.86a2 2 0 00-3.42 0z"/><line x1="12" y1="9" x2="12" y2="13"/><line x1="12" y1="17" x2="12.01" y2="17"/></svg>',
 };
 
-function showToast(message, type = 'default', duration = 3000) {
+function showToast(message, type = 'default', duration = 3000, onUndo = null) {
   const container = document.getElementById('toast-container');
   if (!container) return;
 
+  // Max. 3 gleichzeitige Toasts: ältesten entfernen falls Limit erreicht
+  const existing = container.querySelectorAll('.toast');
+  if (existing.length >= 3) existing[0].remove();
+
   const toast = document.createElement('div');
   toast.className = `toast ${type !== 'default' ? `toast--${type}` : ''}`;
   toast.setAttribute('role', 'alert');
@@ -412,8 +416,20 @@ function showToast(message, type = 'default', duration = 3000) {
   toast.innerHTML = icon; // eslint-disable-line no-unsanitized/property -- static SVG only
   toast.appendChild(span);
 
+  if (typeof onUndo === 'function') {
+    const undoBtn = document.createElement('button');
+    undoBtn.className = 'toast__undo';
+    undoBtn.textContent = t('common.undo');
+    undoBtn.addEventListener('click', () => {
+      clearTimeout(dismissTimer);
+      toast.remove();
+      onUndo();
+    });
+    toast.appendChild(undoBtn);
+  }
+
   container.appendChild(toast);
-  setTimeout(() => {
+  const dismissTimer = setTimeout(() => {
     toast.classList.add('toast--out');
     toast.addEventListener('animationend', () => toast.remove(), { once: true });
   }, duration);