CUB-204: wire WS client as primary, REST poller as fallback

- Rename GatewayURL/GatewayPollInterval → GatewayRestURL/GatewayRestPollInterval
- Change Docker-aware defaults (host.docker.internal instead of localhost)
- Client.Start() waits for WS readiness (30s timeout), falls back to REST
- Client.SetWSClient()/MarkWSReady() for WS→REST coordination
- WSClient.SetRESTClient() so WS notifies REST on successful handshake
- main.go wires both clients: WS primary, REST fallback with cross-references
- .env.example documents WS_GATEWAY_URL, GATEWAY_TOKEN, REST fallback vars
- docker-compose.yml adds WS_GATEWAY_URL and GATEWAY_TOKEN env vars
- reference/CONTROL_CENTER_CONTEXT.md documents architecture and startup sequence

go-backend/cmd/server/main.go

@@ -63,25 +63,30 @@ func main() {
 		Broker:     broker,
 	})
 
-	// ── Gateway client (polls OpenClaw for agent states) ───────────────────
-	gwClient := gateway.NewClient(gateway.Config{
-		URL:          cfg.GatewayURL,
-		PollInterval: cfg.GatewayPollInterval,
-	}, agentRepo, broker)
-
-	// ── WebSocket client (connects to OpenClaw gateway WS v3) ─────────────
+	// ── Gateway clients (WS primary, REST fallback) ───────────────────
+	// WS gateway client (primary path)
 	wsClient := gateway.NewWSClient(gateway.WSConfig{
 		URL:       cfg.WSGatewayURL,
 		AuthToken: cfg.WSGatewayToken,
 	}, agentRepo, broker, logger)
 
+	// REST gateway client (fallback — only polls if WS fails to connect)
+	gwClient := gateway.NewClient(gateway.Config{
+		URL:          cfg.GatewayRestURL,
+		PollInterval: cfg.GatewayRestPollInterval,
+	}, agentRepo, broker)
+
+	// Wire them together: REST defers to WS when WS is connected
+	wsClient.SetRESTClient(gwClient)
+	gwClient.SetWSClient(wsClient)
+
 	ctx, cancel := context.WithCancel(context.Background())
 	defer cancel()
 
-	go gwClient.Start(ctx)
-
-	// Start WS client in background; logs connection status
+	// Start WS client first (primary)
 	go wsClient.Start(ctx)
+	// Start REST client (will wait for WS, then stand down or fall back)
+	go gwClient.Start(ctx)
 
 	// ── Server ─────────────────────────────────────────────────────────────
 	srv := &http.Server{