Add Gateway device inventory panel

src/server/dataplaneClient.js

@@ -43,6 +43,7 @@ export function createDataplaneClient(socketPath, send = request) {
     get running() { return Boolean(current.running); },
     get startedAt() { return current.startedAt || null; },
     refresh: () => update('/status', 'GET'),
+    observeDevices: () => send(socketPath, '/devices', 'GET'),
     apply: () => update('/apply', 'POST'),
     restart: () => update('/restart', 'POST'),
     stop: () => update('/stop', 'POST'),