Implement Phase 2: product archive and shop loop templates (Bootstrap 5)

Add 15 Twig template overrides for the product archive and shop loop:
- archive-product: 3+9 grid layout with optional filter sidebar
- content-product: card component with hook-based content injection
- content-product-cat: category card with thumbnail
- product-searchform: input-group with search icon button
- loop/loop-start, loop-end: responsive row-cols grid
- loop/header: archive title with description hook
- loop/result-count: showing X-Y of Z with aria-relevant
- loop/orderby: form-select-sm sort dropdown
- loop/pagination: delegates to components/pagination.html.twig
- loop/no-products-found: alert-info empty state
- loop/add-to-cart: btn-primary-sm with AJAX data attributes
- loop/price: fw-semibold with sale/regular markup
- loop/rating: Bootstrap Icon stars (full, half, empty)
- loop/sale-flash: badge bg-danger positioned overlay

CSS additions: product card hover, sale badge z-index, star rating sizing,
price del/ins styling, WooCommerce grid reset.

Co-Authored-By: Claude Opus 4.6 <noreply@anthropic.com>

templates/loop/no-products-found.html.twig

@@ -0,0 +1,17 @@
+{#
+ # No Products Found (Bootstrap 5 Override)
+ #
+ # Displayed when the product archive has no results.
+ #
+ # WooCommerce PHP equivalent: loop/no-products-found.php
+ #
+ # @package WcBootstrap
+ # @since 0.1.0
+ #}
+
+<div class="woocommerce-no-products-found">
+    <div class="alert alert-info" role="alert">
+        <i class="bi bi-info-circle me-2" aria-hidden="true"></i>
+        {{ __('No products were found matching your selection.') }}
+    </div>
+</div>