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/add-to-cart.html.twig

@@ -0,0 +1,47 @@
+{#
+ # Loop Add to Cart Button (Bootstrap 5 Override)
+ #
+ # Renders the add-to-cart button within the product loop.
+ #
+ # Expected context:
+ #   product - WC_Product object with:
+ #     .add_to_cart_url()     - Add to cart URL
+ #     .add_to_cart_text()    - Button label
+ #     .is_purchasable()      - Whether product can be purchased
+ #     .is_in_stock()         - Whether product is in stock
+ #     .supports('ajax_add_to_cart') - Whether AJAX add to cart is supported
+ #     .get_id()              - Product ID
+ #   args - Array with:
+ #     .quantity              - Quantity (default: 1)
+ #     .class                 - CSS classes
+ #     .attributes            - Additional HTML attributes
+ #     .aria-describedby_text - Accessibility description
+ #
+ # WooCommerce PHP equivalent: loop/add-to-cart.php
+ #
+ # @package WcBootstrap
+ # @since 0.1.0
+ #}
+
+{% set quantity = args.quantity|default(1) %}
+{% set btn_class = 'btn btn-primary btn-sm w-100' %}
+
+<a href="{{ product.add_to_cart_url()|esc_url }}"
+   class="{{ btn_class }} {{ args.class|default('') }}"
+   data-quantity="{{ quantity }}"
+   data-product_id="{{ product.get_id() }}"
+   {% if args.attributes is defined %}
+       {% for attr, value in args.attributes %}
+           {{ attr }}="{{ value|esc_attr }}"
+       {% endfor %}
+   {% endif %}
+   aria-label="{{ product.add_to_cart_text()|esc_attr }}"
+   rel="nofollow">
+    {{ product.add_to_cart_text() }}
+</a>
+
+{% if args['aria-describedby_text'] is defined and args['aria-describedby_text'] %}
+    <span id="woocommerce_loop_add_to_cart_link_describedby_{{ product.get_id() }}" class="visually-hidden">
+        {{ args['aria-describedby_text'] }}
+    </span>
+{% endif %}