feat: module toggles in POS config and Instance Manager

- Add GET/PUT /pos/api/config/modules endpoints in POS config_bp.py
- Update sidebar.js to filter nav items based on enabled modules
- Add Modules section to POS config.html with toggles for WhatsApp, Marketplace, MercadoLibre
- Add module load/save logic to POS config.js
- Preload modules in app-init.js for sidebar caching

- Add tenant module management to Instance Manager
  - get_tenant_modules / update_tenant_modules in tenant_service.py
  - GET/PUT /api/tenants/<id>/modules endpoints in tenants_bp.py
  - Add modules modal to manager index.html
  - Add module editing UI and logic to manager.js
  - Add toggle-switch CSS to manager.css

pos/services/pos_engine.py

@@ -440,6 +440,13 @@ def process_sale(conn, sale_data):
     except Exception:
         pass  # Savings errors never block sales
 
+    # WhatsApp learning hook (non-blocking)
+    try:
+        from services.wa_learning import check_learning_resolution
+        check_learning_resolution(sale_id, customer_id, conn)
+    except Exception:
+        pass  # Learning errors never block sales
+
     return {
         'id': sale_id,
         'branch_id': branch_id,