Add Bootstrap 5 single product page layout

Add two-column responsive grid (image gallery + product summary) for
single product pages, following the same bridge pattern used for
product archives.

Key changes:
- Create content-single-product.php bridge and Twig layout template
- Add single product renderer at template_redirect priority 11
- Disable WooCommerce block compatibility layer that strips classic
  hooks when parent theme has theme.json
- Move PHP templates to woocommerce/ subfolder for cleaner structure
- Fix Twig templates to self-compute context data not passed by
  wc_get_template() (tabs, short-description, meta, rating)
- Fix Underscore.js triple-brace syntax conflict in variation template
  by wrapping in {% verbatim %}

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

templates/single-product/tabs/tabs.html.twig

@@ -16,7 +16,12 @@
  # @since 0.1.0
  #}
 
-{% if product_tabs is defined and product_tabs|length > 0 %}
+{# Compute tabs from filter when not passed as context (wc_get_template passes no args). #}
+{% if product_tabs is not defined %}
+    {% set product_tabs = apply_filters('woocommerce_product_tabs', {}) %}
+{% endif %}
+
+{% if product_tabs|length > 0 %}
     <div class="woocommerce-tabs wc-tabs-wrapper mt-5">
         {# Tab navigation #}
         <ul class="nav nav-tabs" id="productTabs" role="tablist">