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/payment-method.html.twig

@@ -0,0 +1,46 @@
+{#
+ # Single Payment Method (Bootstrap 5 Override)
+ #
+ # Renders a payment gateway as a list-group-item with radio and description.
+ #
+ # Expected context:
+ #   gateway - WC_Payment_Gateway object with:
+ #     .id                - Gateway ID
+ #     .get_title()       - Gateway title
+ #     .get_icon()        - Gateway icon HTML
+ #     .has_fields()      - Whether gateway has inline fields
+ #     .get_description() - Gateway description
+ #     .chosen            - Whether this is the selected gateway
+ #     .payment_fields()  - Renders inline payment fields
+ #
+ # WooCommerce PHP equivalent: checkout/payment-method.php
+ #
+ # @package WcBootstrap
+ # @since 0.1.0
+ #}
+
+<li class="wc_payment_method payment_method_{{ gateway.id|esc_attr }} list-group-item">
+    <div class="form-check">
+        <input type="radio"
+               class="form-check-input input-radio"
+               name="payment_method"
+               id="payment_method_{{ gateway.id|esc_attr }}"
+               value="{{ gateway.id|esc_attr }}"
+               data-order_button_text="{{ gateway.order_button_text|default('')|esc_attr }}"
+               {% if gateway.chosen is defined and gateway.chosen %}checked{% endif %} />
+
+        <label class="form-check-label d-flex align-items-center gap-2" for="payment_method_{{ gateway.id|esc_attr }}">
+            <span>{{ gateway.get_title()|esc_html }}</span>
+            {{ gateway.get_icon()|raw }}
+        </label>
+    </div>
+
+    {% if gateway.has_fields() or gateway.get_description() %}
+        <div class="payment_box payment_method_{{ gateway.id|esc_attr }} mt-2 ps-4{% if not gateway.chosen|default(false) %} d-none{% endif %}">
+            {% if gateway.get_description() %}
+                <p class="small text-body-secondary mb-2">{{ gateway.get_description()|wp_kses_post }}</p>
+            {% endif %}
+            {{ gateway.payment_fields() }}
+        </div>
+    {% endif %}
+</li>