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>

PLAN.md

@@ -519,15 +519,15 @@ Track completion per file. Mark with `[x]` when done.
 
 ### Phase 1 -- Global & Notices
 
-- [ ] `global/wrapper-start.html.twig`
-- [ ] `global/wrapper-end.html.twig`
-- [ ] `global/breadcrumb.html.twig`
-- [ ] `global/sidebar.html.twig`
-- [ ] `global/quantity-input.html.twig`
-- [ ] `global/form-login.html.twig`
-- [ ] `notices/notice.html.twig`
-- [ ] `notices/error.html.twig`
-- [ ] `notices/success.html.twig`
+- [x] `global/wrapper-start.html.twig`
+- [x] `global/wrapper-end.html.twig`
+- [x] `global/breadcrumb.html.twig`
+- [x] `global/sidebar.html.twig`
+- [x] `global/quantity-input.html.twig`
+- [x] `global/form-login.html.twig`
+- [x] `notices/notice.html.twig`
+- [x] `notices/error.html.twig`
+- [x] `notices/success.html.twig`
 
 ### Phase 2 -- Archive & Loop