style(openai-ws): 修复 passthrough_relay gofmt 对齐

PR #2444 引入的 activeTurn 字段未按 gofmt 对齐，导致 golangci-lint
报 gofmt 错误。运行 gofmt -w 调整字段类型对齐到与同结构其他字段一致。

backend/internal/service/openai_ws_v2/passthrough_relay.go

@@ -82,7 +82,7 @@ type relayState struct {
 	terminalEventType string
 	firstTokenMs      *int
 	turnTimingByID    map[string]*relayTurnTiming
-	activeTurn *relayTurnTiming
+	activeTurn        *relayTurnTiming
 }
 
 type relayExitSignal struct {