feat(builder): visual homepage blocks, merchant-language widget settings, real carousel arrows

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

P0 user feedback: homepage builder showed raw section.id like 'section-hero'/'section-categories'; hero widget exposed 'full-bleed'/'boxed' and raw px/vh as free text with no explanation; Overlay/Autoplay toggles made no sense without a slides concept; product carousel widgets rendered arrows nowhere near a working carousel.

Homepage section (sections list -> visual blocks):
- Replaced raw section.id display with a merchant-facing block catalog (icon + name + one-line explanation) for hero/categories/featured-products/product-carousel/recently-viewed/banner/partners/custom-html
- Added block catalog picker to append new blocks (was fixed at whatever the seed data had - task asked 'what if we add manually? not fixed 3')
- Added duplicate and remove per block, alongside the existing drag-to-reorder
- Verified in browser: labels render correctly, add-block and duplicate both confirmed working end-to-end

Widgets section (hero widget):
- 'Layout' free-text replaced with a select (Full width / Boxed) instead of typing 'full-bleed'/'boxed' blind
- 'Height' free-text replaced with a select (Compact/Medium/Tall/Full screen) mapped to real vh values
- New Slides editor: title/subtitle pairs an admin can add/remove: this is the actual multi-slide data the Overlay/Autoplay toggles were referring to with nothing to point at before
- HeroWidgetData contract gains slides[]/autoplay; HeroWidgetComponent now renders a real rotator (dots, click-to-jump, autoplay interval) when more than one slide exists - previously autoplay/overlay props existed but there was no slideshow behavior anywhere to control

Carousel arrows root cause and fix:
- widget-manifest.json offers 'carousel' as a layout option for product-collection/product-carousel widgets, and the admin UI let you select it, but ProductCarouselWidgetComponent always rendered a static CSS grid regardless - there was no carousel implementation to have arrows in the first place
- Now renders a real horizontally-scrollable strip with working prev/next buttons (native scrollBy, disabled at each end) when section.layout.strategy === 'carousel'; falls back to the existing grid otherwise
- Confirmed src/app/components/items-carousel (a PrimeNG p-carousel) is dead code, not wired into any route or widget - not the source of the reported bug

New builder.* i18n keys (en/ru/hy), zero duplicate-key collisions verified via scan

src/app/features/project-editor/sections/widgets-section.component.scss

@@ -94,3 +94,24 @@
     color: var(--text-light);
   }
 }
+
+.widget-card__subheading { margin: 12px 0 4px; font-size: 0.9rem; }
+
+.hero-slide-row {
+  display: flex;
+  gap: 8px;
+  align-items: center;
+  margin-bottom: 6px;
+
+  app-input { flex: 1; }
+}
+
+.hero-slide-row__remove {
+  border: none;
+  background: transparent;
+  cursor: pointer;
+  color: var(--text-secondary, #6b7280);
+  font-size: 1rem;
+
+  &:hover { color: var(--danger-color, #c0392b); }
+}