fix: manifest-aware layout picker, real carousel items-per-page, hero arrows/swipe/2-panel

Sprint E: homepage section editor now filters the layout-strategy picker
to each widget's widget-manifest.json supportedLayouts instead of always
showing all 5 strategies. columns field gated to widgets that read it
(hero, product-collection carousel).

Sprint F: closes client bug report (no items-per-page control, hero
carousel not manually/automatically scrollable, no 1-2 slide big-carousel
option). Product carousel item width now driven by layout.columns
(reused, was already editable but dead). Hero widget gains prev/next
arrows, touch swipe, and 1-2 panel mode via the same field.

Co-Authored-By: Claude Sonnet 5 <noreply@anthropic.com>

src/app/i18n/translations.ts

@@ -1115,6 +1115,8 @@ export interface Translations {
     slidesLabel: string;
     previousProducts: string;
     nextProducts: string;
+    previousSlide: string;
+    nextSlide: string;
     closeDialog: string;
     dismiss: string;
     qrCode: string;