fix(ui): replace native confirm()/alert() with shared dialogs and toasts

New app-confirm-dialog (wraps existing app-dialog + app-button) replaces
every native confirm() across media library bulk-delete, static pages
editor (delete/bulk-delete), builder save-bar (publish/reset-draft),
project-editor-page (reset-section), homepage/languages/widgets sections
(remove block/language/widget), and cart (clear-cart).

Cart's native alert() calls (delivery/terms validation, email send
success/failure) now route through the existing UserNotificationService
toast pipeline instead.

No native confirm()/alert()/prompt() remain in production UI.

src/app/i18n/en.ts

@@ -1097,6 +1097,8 @@ export const en: Translations = {
     qrCode: 'QR Code',
     bankCardPayment: 'Bank card payment',
     guest: 'Guest',
+    cancel: 'Cancel',
+    confirm: 'Confirm',
   },
   location: {
     allRegions: 'All regions',