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

manager/services/tenant_service.py

@@ -311,6 +311,55 @@ def get_tenant_login_url(subdomain):
     return f"https://{subdomain}.{domain}/pos/login"
 
 
+def get_tenant_modules(tenant_id):
+    """Get enabled modules for a tenant from tenant_config."""
+    tenant = get_tenant(tenant_id)
+    if not tenant:
+        raise ValueError("Tenant not found")
+    db_name = tenant["db_name"]
+    dsn = TENANT_DB_URL_TEMPLATE.format(db_name=db_name)
+    conn = psycopg2.connect(dsn)
+    cur = conn.cursor()
+    try:
+        modules = {}
+        for key in ["module_whatsapp", "module_marketplace", "module_meli"]:
+            cur.execute("SELECT value FROM tenant_config WHERE key = %s", (key,))
+            row = cur.fetchone()
+            modules[key.replace("module_", "")] = (row[0] or "").lower() == "true" if row else True
+        return modules
+    finally:
+        cur.close()
+        conn.close()
+
+
+def update_tenant_modules(tenant_id, modules):
+    """Update enabled modules for a tenant in tenant_config."""
+    tenant = get_tenant(tenant_id)
+    if not tenant:
+        raise ValueError("Tenant not found")
+    db_name = tenant["db_name"]
+    dsn = TENANT_DB_URL_TEMPLATE.format(db_name=db_name)
+    conn = psycopg2.connect(dsn)
+    cur = conn.cursor()
+    try:
+        key_map = {
+            "whatsapp": "module_whatsapp",
+            "marketplace": "module_marketplace",
+            "meli": "module_meli",
+        }
+        for field, key in key_map.items():
+            value = "true" if modules.get(field) else "false"
+            cur.execute("""
+                INSERT INTO tenant_config (key, value) VALUES (%s, %s)
+                ON CONFLICT (key) DO UPDATE SET value = EXCLUDED.value
+            """, (key, value))
+        conn.commit()
+        return {"success": True, "tenant_id": tenant_id, "modules": modules}
+    finally:
+        cur.close()
+        conn.close()
+
+
 def get_dashboard_stats():
     """Global stats for the manager dashboard."""
     conn = get_master_conn()