Implement Phase 1: global templates and notices (Bootstrap 5)

Add 9 Twig template overrides for WooCommerce's global and notice templates:
- global/wrapper-start, wrapper-end: conditional container with _theme_wrapped
- global/breadcrumb: Bootstrap breadcrumb component with aria-current
- global/sidebar: offcanvas-lg for mobile, standard aside for desktop
- global/quantity-input: input-group with +/- buttons
- global/form-login: responsive form with form-control, form-check
- notices/notice, error, success: Bootstrap alert-dismissible with icons

Supporting changes:
- assets/js/quantity.js: +/- button handler respecting min/max/step
- assets/css/wc-bootstrap.css: WooCommerce notice fallback styles, spinner removal
- functions.php: register quantity.js script

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

templates/global/sidebar.html.twig

@@ -0,0 +1,40 @@
+{#
+ # Shop Sidebar (Bootstrap 5 Override)
+ #
+ # Renders the WooCommerce shop sidebar using Bootstrap 5 offcanvas for mobile
+ # and a standard aside column for desktop.
+ #
+ # Expected context:
+ #   sidebar_content - Pre-rendered sidebar widget HTML (from get_sidebar('shop'))
+ #
+ # WooCommerce PHP equivalent: global/sidebar.php
+ #
+ # @package WcBootstrap
+ # @since 0.1.0
+ #}
+
+{% if sidebar_content is defined and sidebar_content %}
+    {# Mobile: offcanvas trigger button (visible below lg breakpoint) #}
+    <button class="btn btn-outline-secondary d-lg-none mb-3"
+            type="button"
+            data-bs-toggle="offcanvas"
+            data-bs-target="#shopSidebar"
+            aria-controls="shopSidebar">
+        <i class="bi bi-funnel" aria-hidden="true"></i>
+        {{ __('Filters') }}
+    </button>
+
+    {# Mobile: offcanvas panel #}
+    <div class="offcanvas offcanvas-start offcanvas-lg"
+         tabindex="-1"
+         id="shopSidebar"
+         aria-labelledby="shopSidebarLabel">
+        <div class="offcanvas-header">
+            <h5 class="offcanvas-title" id="shopSidebarLabel">{{ __('Filters') }}</h5>
+            <button type="button" class="btn-close" data-bs-dismiss="offcanvas" aria-label="{{ __('Close') }}"></button>
+        </div>
+        <div class="offcanvas-body">
+            {{ sidebar_content|raw }}
+        </div>
+    </div>
+{% endif %}