feat: MercadoLibre integration + inventory bulk publish + WhatsApp bridge fixes

- Add MercadoLibre OAuth, listings, orders, webhooks and category search
- New marketplace_external_bp.py, meli_service.py, marketplace_external_service.py
- New marketplace_external.html/js with ML management UI
- Inventory: bulk publish to ML with category autocomplete, listing type and shipping selectors
- Inventory: new .btn--meli styles, select/label CSS fixes
- WhatsApp bridge: rate limiting, 440/515/408 error handling, stale watchdog
- DB migration v3.4_meli_integration.sql for marketplace_listings, orders, sync_queue
- Add Celery tasks for ML sync and webhook processing
- Sidebar: MercadoLibre navigation link

pos/static/js/sidebar.js

@@ -29,6 +29,7 @@
             { name: _t('customers'), href: '/pos/customers', icon: '<path d="M17 21v-2a4 4 0 0 0-4-4H5a4 4 0 0 0-4 4v2"/><circle cx="9" cy="7" r="4"/><path d="M23 21v-2a4 4 0 0 0-3-3.87M16 3.13a4 4 0 0 1 0 7.75"/>' },
             { name: 'Cotizaciones', href: '/pos/quotations', icon: '<path d="M14 2H6a2 2 0 0 0-2 2v16a2 2 0 0 0 2 2h12a2 2 0 0 0 2-2V8z"/><polyline points="14 2 14 8 20 8"/><line x1="9" y1="15" x2="15" y2="15"/><line x1="12" y1="12" x2="12" y2="18"/>' },
             { name: 'Marketplace', href: '/pos/marketplace', icon: '<circle cx="9" cy="21" r="1"/><circle cx="20" cy="21" r="1"/><path d="M1 1h4l2.68 13.39a2 2 0 0 0 2 1.61h9.72a2 2 0 0 0 2-1.61L23 6H6"/>' },
+            { name: 'MercadoLibre', href: '/pos/marketplace-external', icon: '<rect x="2" y="3" width="20" height="14" rx="2"/><path d="M8 21h8M12 17v4"/>' },
             { name: _t('invoicing'), href: '/pos/invoicing', icon: '<path d="M14 2H6a2 2 0 0 0-2 2v16a2 2 0 0 0 2 2h12a2 2 0 0 0 2-2V8z"/><polyline points="14 2 14 8 20 8"/><line x1="16" y1="13" x2="8" y2="13"/><line x1="16" y1="17" x2="8" y2="17"/><polyline points="10 9 9 9 8 9"/>' },
             { name: _t('accounting'), href: '/pos/accounting', icon: '<line x1="12" y1="1" x2="12" y2="23"/><path d="M17 5H9.5a3.5 3.5 0 0 0 0 7h5a3.5 3.5 0 0 1 0 7H6"/>' },
             { name: _t('reports'), href: '/pos/reports', icon: '<line x1="18" y1="20" x2="18" y2="10"/><line x1="12" y1="20" x2="12" y2="4"/><line x1="6" y1="20" x2="6" y2="14"/>' },
@@ -180,4 +181,7 @@
     window.toggleSidebar = toggleSidebar;
     window.closeSidebar = closeSidebar;
 
+    // Reveal sidebar smoothly after replacement to avoid flash/stun
+    document.body.classList.add('sidebar-ready');
+
 })();