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/add-to-cart/variation.html.twig

@@ -11,6 +11,7 @@
  # @since 0.1.0
  #}
 
+{% verbatim %}
 <script type="text/template" id="tmpl-variation-template">
     <div class="woocommerce-variation-description mb-2">
         {{{ data.variation.variation_description }}}
@@ -22,6 +23,7 @@
         {{{ data.variation.availability_html }}}
     </div>
 </script>
+{% endverbatim %}
 
 <script type="text/template" id="tmpl-unavailable-variation-template">
     <p class="alert alert-warning mb-0">