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/checkout/form-shipping.html.twig

@@ -0,0 +1,69 @@
+{#
+ # Shipping Form (Bootstrap 5 Override)
+ #
+ # Renders shipping address fields with "ship to different address" toggle.
+ #
+ # Expected context:
+ #   checkout        - WC_Checkout object
+ #   shipping_fields - Array of shipping field configs
+ #   order_fields    - Array of order note fields
+ #
+ # WooCommerce PHP equivalent: checkout/form-shipping.php
+ #
+ # @package WcBootstrap
+ # @since 0.1.0
+ #}
+
+<div class="woocommerce-shipping-fields">
+    <div class="card shadow-sm mb-4">
+        <div class="card-header">
+            <div class="form-check mb-0">
+                <input class="form-check-input"
+                       type="checkbox"
+                       name="ship_to_different_address"
+                       id="ship-to-different-address-checkbox"
+                       value="1"
+                       {{ ship_to_different_address|default(false) ? 'checked' : '' }} />
+                <label class="form-check-label h5 mb-0" for="ship-to-different-address-checkbox">
+                    {{ __('Ship to a different address?') }}
+                </label>
+            </div>
+        </div>
+
+        <div class="card-body shipping_address collapse{% if ship_to_different_address|default(false) %} show{% endif %}">
+            {{ do_action('woocommerce_before_checkout_shipping_form', checkout) }}
+
+            <div class="woocommerce-shipping-fields__field-wrapper row g-3">
+                {% if shipping_fields is defined %}
+                    {% for key, field in shipping_fields %}
+                        {{ woocommerce_form_field(key, field, checkout.get_value(key)) }}
+                    {% endfor %}
+                {% endif %}
+            </div>
+
+            {{ do_action('woocommerce_after_checkout_shipping_form', checkout) }}
+        </div>
+    </div>
+</div>
+
+{# Order notes #}
+<div class="woocommerce-additional-fields mb-4">
+    {{ do_action('woocommerce_before_order_notes', checkout) }}
+
+    {% if order_fields is defined and order_fields|length > 0 %}
+        <div class="card shadow-sm">
+            <div class="card-header">
+                <h3 class="h5 mb-0">{{ __('Additional information') }}</h3>
+            </div>
+            <div class="card-body">
+                <div class="woocommerce-additional-fields__field-wrapper">
+                    {% for key, field in order_fields %}
+                        {{ woocommerce_form_field(key, field, checkout.get_value(key)) }}
+                    {% endfor %}
+                </div>
+            </div>
+        </div>
+    {% endif %}
+
+    {{ do_action('woocommerce_after_order_notes', checkout) }}
+</div>