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

dashboard/admin.html

@@ -92,6 +92,14 @@
                     <span class="badge" id="pendingUsersBadge" style="display:none; background:var(--warning); color:#000; font-size:0.7rem; padding:2px 6px; border-radius:10px; margin-left:auto;"></span>
                 </div>
             </div>
+
+            <div class="sidebar-section">
+                <h3>Tenants</h3>
+                <div class="sidebar-item" data-section="tenants">
+                    <span class="icon">🏢</span>
+                    <span>Módulos</span>
+                </div>
+            </div>
         </aside>
 
         <!-- Main Content -->
@@ -660,6 +668,35 @@
                 </div>
             </section>
 
+            <!-- Tenants / Modules Section -->
+            <section id="section-tenants" class="admin-section">
+                <div class="page-header">
+                    <h1 class="page-title">Configuración de Módulos por Tenant</h1>
+                </div>
+                <div class="card">
+                    <div class="card-header">
+                        <h2 class="card-title">Tenants Activos</h2>
+                    </div>
+                    <div style="overflow-x:auto;">
+                        <table class="data-table">
+                            <thead>
+                                <tr>
+                                    <th>ID</th>
+                                    <th>Nombre</th>
+                                    <th>WhatsApp</th>
+                                    <th>Marketplace</th>
+                                    <th>MercadoLibre</th>
+                                    <th>Acciones</th>
+                                </tr>
+                            </thead>
+                            <tbody id="tenantsTable">
+                                <tr><td colspan="6" class="loading"><div class="spinner"></div></td></tr>
+                            </tbody>
+                        </table>
+                    </div>
+                </div>
+            </section>
+
         </main>
     </div>