Security audit fixes: fn() whitelist, escaping, and performance (v0.1.4)

- WooCommerceExtension: ALLOWED_FUNCTIONS whitelist for fn() Twig function
- Notice templates: data attributes use wp_kses_post instead of raw
- Search form: esc_attr on search query value attribute
- Per-request ContextBuilder caching via static variable
- Shared wc_bootstrap_render_in_page_shell() helper (DRY)
- Removed unused WC_BOOTSTRAP_VERSION and WC_BOOTSTRAP_URL constants

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

templates/notices/notice.html.twig

@@ -17,7 +17,7 @@
 {% if notices is defined and notices|length > 0 %}
     {% for notice in notices %}
         <div class="alert alert-info alert-dismissible fade show woocommerce-info"
-             {{ notice.data|default('')|raw }}
+             {{ notice.data|default('')|wp_kses_post }}
              role="status">
             <i class="bi bi-info-circle me-2" aria-hidden="true"></i>
             {{ notice.notice|raw }}