chore: WebSocket 演示地址切换为 wss://echo.websocket.org（含存量数据迁移）

packages/ui/src/components/editors/WebsocketEditor.tsx

@@ -31,7 +31,7 @@ export function WebsocketEditor({ node }: { node: WebsocketApiNode }) {
         <span className="ops-chip inline-flex items-center gap-1" style={{ padding: "2px 10px" }}><Icon name="zap" size={13} /> WS</span>
         <VarHintInput
           className="ops-input flex-1 font-mono text-[13px]"
-          placeholder="wss://echo.websocket.events"
+          placeholder="wss://echo.websocket.org"
           value={data.url}
           onChange={(v) => patch({ url: v })}
         />