Klyo Marketplace integration for plugin discovery and reviews

Gateway can now connect to Klyo Marketplace to register the install, sync available plugins, and submit star-rating reviews from the admin console. Plugin detail pages show install and uninstall toggles, ratings, and paginated reviews. Heartbeat traffic to the marketplace is opt-in and scoped to the configured license key.

No action required. Set MARKETPLACE_ENABLED=true and a marketplace license key to turn it on. Existing installs continue to operate without it.