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>

assets/css/wc-bootstrap.css

@@ -37,19 +37,56 @@
 */
 
 /* ==========================================================================
-   Notification Overrides
-   Map plugin notification classes to Bootstrap alert styles.
+   WooCommerce Notice Overrides
+   Map WooCommerce notice classes to Bootstrap alert styles as fallback
+   when notices are rendered outside our Twig templates.
    ========================================================================== */
 
-/* Example: Map plugin .my-notification to Bootstrap alert
-.my-notification {
+.woocommerce-info,
+.woocommerce-message,
+.woocommerce-error {
     position: relative;
-    padding: 1rem 1rem;
+    padding: 1rem 3rem 1rem 1rem;
     margin-bottom: 1rem;
     border: 1px solid transparent;
     border-radius: var(--bs-border-radius);
 }
-*/
+
+.woocommerce-info {
+    color: var(--bs-info-text-emphasis);
+    background-color: var(--bs-info-bg-subtle);
+    border-color: var(--bs-info-border-subtle);
+}
+
+.woocommerce-message {
+    color: var(--bs-success-text-emphasis);
+    background-color: var(--bs-success-bg-subtle);
+    border-color: var(--bs-success-border-subtle);
+}
+
+.woocommerce-error {
+    color: var(--bs-danger-text-emphasis);
+    background-color: var(--bs-danger-bg-subtle);
+    border-color: var(--bs-danger-border-subtle);
+    list-style: none;
+    padding-left: 1rem;
+}
+
+/* ==========================================================================
+   Quantity Input
+   Sizing for the Bootstrap input-group quantity widget.
+   ========================================================================== */
+
+.quantity.input-group .form-control {
+    /* Remove number input spinners (browser default) */
+    -moz-appearance: textfield;
+}
+
+.quantity.input-group .form-control::-webkit-outer-spin-button,
+.quantity.input-group .form-control::-webkit-inner-spin-button {
+    -webkit-appearance: none;
+    margin: 0;
+}
 
 /* ==========================================================================
    Dark Mode Overrides