Implement Phase 4 & 5: cart and checkout templates (Bootstrap 5, HPOS)

Phase 4 - Cart (9 templates):
- cart: 8+4 column layout, table-responsive items, coupon input-group
- cart-empty: centered empty state with cart-x icon
- cart-item-data: inline dl for variation details
- cart-totals: card with list-group-flush rows, sticky sidebar
- cart-shipping: form-check radio per shipping method
- cross-sells: product loop grid section
- mini-cart: offcanvas-compatible item list with remove buttons
- proceed-to-checkout-button: btn-primary btn-lg w-100
- shipping-calculator: collapsible form with form-select/form-control

Phase 5 - Checkout (12 templates):
- form-checkout: 7+5 column layout, sticky order review sidebar
- form-billing: card with field wrapper, optional account creation
- form-shipping: card with ship-to-different-address collapse toggle
- form-coupon: collapsible input-group with alert-info toggle
- form-login: collapsible login reusing global/form-login.html.twig
- review-order: card with table-sm, tfoot subtotal/shipping/total
- payment: list-group of payment gateways with radio selection
- payment-method: form-check with description collapse
- terms: form-check checkbox with T&C link
- thankyou: HPOS compatible, alert-success + order details list-group
- order-received: confirmation message
- cart-errors: alert-danger with return-to-cart button

All order data accessed via WC_Order methods (HPOS compatible).
CSS additions: cart thumbnail sizing, checkout form field overrides,
payment box transitions, dark mode focus states.

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

templates/cart/cart-shipping.html.twig

@@ -0,0 +1,69 @@
+{#
+ # Cart Shipping Methods (Bootstrap 5 Override)
+ #
+ # Renders available shipping methods as Bootstrap form-check radios.
+ #
+ # Expected context:
+ #   available_methods      - Array of shipping method objects
+ #   chosen_method          - Currently chosen method ID
+ #   formatted_destination  - Formatted shipping address
+ #   has_calculated_shipping - Whether shipping has been calculated
+ #   show_shipping_calculator - Whether to show the calculator
+ #   package_name           - Package name/label
+ #   index                  - Package index
+ #
+ # WooCommerce PHP equivalent: cart/cart-shipping.php
+ #
+ # @package WcBootstrap
+ # @since 0.1.0
+ #}
+
+<div class="woocommerce-shipping-totals shipping">
+    <strong class="d-block mb-2">{{ package_name|default(__('Shipping'))|esc_html }}</strong>
+
+    {% if available_methods is defined and available_methods|length > 0 %}
+        <ul id="shipping_method_{{ index|default(0) }}" class="list-unstyled mb-2">
+            {% for method_id, method in available_methods %}
+                <li class="form-check">
+                    {% if available_methods|length > 1 %}
+                        <input type="radio"
+                               name="shipping_method[{{ index|default(0) }}]"
+                               id="shipping_method_{{ index|default(0) }}_{{ method_id|esc_attr }}"
+                               value="{{ method_id|esc_attr }}"
+                               class="form-check-input shipping_method"
+                               data-index="{{ index|default(0) }}"
+                               {% if method_id == chosen_method %}checked{% endif %} />
+                    {% else %}
+                        <input type="hidden"
+                               name="shipping_method[{{ index|default(0) }}]"
+                               value="{{ method_id|esc_attr }}"
+                               class="shipping_method"
+                               data-index="{{ index|default(0) }}" />
+                    {% endif %}
+                    <label class="form-check-label" for="shipping_method_{{ index|default(0) }}_{{ method_id|esc_attr }}">
+                        {{ method.get_label()|raw }}
+                    </label>
+                    {{ do_action('woocommerce_after_shipping_rate', method, index|default(0)) }}
+                </li>
+            {% endfor %}
+        </ul>
+
+        {% if formatted_destination is defined and formatted_destination %}
+            <p class="woocommerce-shipping-destination small text-body-secondary mb-0">
+                {{ formatted_destination|raw }}
+            </p>
+        {% endif %}
+    {% elseif not has_calculated_shipping|default(false) %}
+        <p class="text-body-secondary small mb-0">
+            {{ __('Shipping costs are calculated during checkout.') }}
+        </p>
+    {% else %}
+        <p class="text-body-secondary small mb-0">
+            {{ __('No shipping options were found.') }}
+        </p>
+    {% endif %}
+
+    {% if show_shipping_calculator|default(false) %}
+        {% include 'cart/shipping-calculator.html.twig' %}
+    {% endif %}
+</div>