Implement Phase 3: single product page templates (Bootstrap 5)

Add 21 Twig template overrides for the single product page:

Product layout:
- product-image: gallery with thumbnail strip, img-fluid rounded
- title: h1 entry-title
- price: fs-3 fw-bold with sale del/ins markup
- short-description: lead text-body-secondary
- meta: dl row with SKU, categories, tags
- rating: Bootstrap Icon stars with half-star, review count link
- stock: badge (bg-success/bg-danger/bg-warning) per status
- sale-flash: badge bg-danger fs-6
- share: hook-only wrapper
- product-attributes: table-sm table-striped

Related/upsells:
- related, up-sells: section with product loop grid

Tabs:
- tabs: nav-tabs + tab-content with fade transitions
- description: tab-pane with prose content
- additional-information: tab-pane with attributes hook

Add to cart (4 product types + variation JS):
- simple: input-group quantity + btn-primary btn-lg
- variable: form-select per attribute + variation display
- grouped: table-borderless with quantity per child product
- external: btn-outline-primary with external link icon
- variation: Underscore.js script templates (Bootstrap-styled)
- variation-add-to-cart-button: quantity + submit with hidden fields

CSS additions: gallery thumbnail hover, variation selector spacing.

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

assets/css/wc-bootstrap.css

@@ -144,6 +144,40 @@
     font-weight: 600;
 }
 
+/* ==========================================================================
+   Product Gallery
+   Thumbnail grid and cursor for single product image gallery.
+   ========================================================================== */
+
+.wc-gallery-thumb {
+    cursor: pointer;
+    opacity: 0.7;
+    transition: opacity 0.15s ease;
+}
+
+.wc-gallery-thumb:hover {
+    opacity: 1;
+}
+
+.woocommerce-product-gallery__image img {
+    width: 100%;
+    height: auto;
+    border-radius: var(--bs-border-radius);
+}
+
+/* ==========================================================================
+   Variation Selectors
+   Spacing for variable product attribute dropdowns.
+   ========================================================================== */
+
+.variations_form .reset_variations {
+    font-size: 0.875rem;
+}
+
+.single_variation_wrap .woocommerce-variation {
+    margin-bottom: 1rem;
+}
+
 /* ==========================================================================
    WooCommerce Grid Override
    Reset WooCommerce's default grid to let Bootstrap handle layout.