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/static/js/app-init.js

@@ -180,4 +180,18 @@
         permissions: payload.permissions || []
     };
 
+    // ─── Preload enabled modules for sidebar filtering ───
+    try {
+        fetch('/pos/api/config/modules', {
+            headers: { 'Authorization': 'Bearer ' + token }
+        }).then(function(r) {
+            if (r.ok) return r.json();
+        }).then(function(data) {
+            if (data) {
+                localStorage.setItem('pos_modules', JSON.stringify(data));
+                window.POS_USER.modules = data;
+            }
+        }).catch(function() {});
+    } catch(e) {}
+
 })();