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/pages/contacts.js

@@ -5,7 +5,7 @@
  */
 
 import { api } from '/api.js';
-import { openModal as openSharedModal, closeModal } from '/components/modal.js';
+import { openModal as openSharedModal, closeModal, confirmModal } from '/components/modal.js';
 import { stagger, vibrate } from '/utils/ux.js';
 import { t } from '/i18n.js';
 import { esc } from '/utils/html.js';
@@ -304,7 +304,6 @@ function openContactModal({ mode, contact = null }) {
       panel.querySelector('#cm-cancel').addEventListener('click', closeModal);
 
       panel.querySelector('#cm-delete')?.addEventListener('click', async () => {
-        if (!confirm(t('contacts.deletePersonConfirm', { name: contact.name }))) return;
         closeModal();
         await deleteContact(contact.id);
       });
@@ -351,7 +350,7 @@ function openContactModal({ mode, contact = null }) {
 }
 
 async function deleteContact(id) {
-  if (!confirm(t('contacts.deleteConfirm'))) return;
+  if (!await confirmModal(t('contacts.deleteConfirm'), { danger: true, confirmLabel: t('common.delete') })) return;
   try {
     await api.delete(`/contacts/${id}`);
     state.contacts = state.contacts.filter((c) => c.id !== id);