fix: handle URL tab parameter in admin pricing page

- Parse URLSearchParams to detect ?tab=pricelists on page load
- Load tab from URL or default to 'alerts'
- Fixes redirect from /pricelists to /admin/pricing?tab=pricelists

This resolves the critical UX issue where users redirected from
/pricelists would see the 'alerts' tab instead of 'pricelists'.

Co-Authored-By: Claude Sonnet 4.5 <noreply@anthropic.com>

web/templates/admin_pricing.html

@@ -877,7 +877,10 @@ function renderAllConfigs(configs) {
 }
 
 document.addEventListener('DOMContentLoaded', () => {
-    loadTab('alerts');
+    // Check URL params for initial tab
+    const urlParams = new URLSearchParams(window.location.search);
+    const initialTab = urlParams.get('tab') || 'alerts';
+    loadTab(initialTab);
 
     // Add event listeners for preview updates
     document.getElementById('modal-period').addEventListener('change', fetchPreview);