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/pages/cart/cart.component.html

@@ -293,4 +293,13 @@
 
 <app-telegram-login />
 
+<app-confirm-dialog
+  [open]="clearCartConfirmOpen()"
+  [titleText]="'cart.confirmClear' | translate"
+  [message]="'cart.confirmClear' | translate"
+  [destructive]="true"
+  (confirmed)="confirmClearCart()"
+  (cancelled)="clearCartConfirmOpen.set(false)"
+/>
+