refactor: added `robots.txt` to disallow indexing

src/PortalTask.h

@@ -859,6 +859,7 @@ protected:
       }
     });
 
+    this->webServer->serveStatic("/robots.txt", LittleFS, "/static/robots.txt", PORTAL_CACHE);
     this->webServer->serveStatic("/favicon.ico", LittleFS, "/static/images/favicon.ico", PORTAL_CACHE);
     this->webServer->serveStatic("/static", LittleFS, "/static", PORTAL_CACHE);
   }