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/blueprints/pos_bp.py

@@ -1864,6 +1864,14 @@ def complete_layaway(layaway_id):
                    new_value={'sale_id': sale['id'], 'total': total})
 
         conn.commit()
+
+        # WhatsApp learning hook (non-blocking)
+        try:
+            from services.wa_learning import check_learning_resolution
+            check_learning_resolution(sale['id'], cust_id, conn)
+        except Exception:
+            pass
+
         cur.close(); conn.close()
         return jsonify(sale), 201