feat(openai-ws): 合并 WS v2 透传模式与前端 ws mode

新增 OpenAI WebSocket v2 passthrough relay 数据面与服务适配层，
支持按账号 ws mode 在 ctx_pool 与 passthrough 间路由。

同步调整前端 OpenAI ws mode 选项为 off/ctx_pool/passthrough，
并补充 i18n 文案与对应单测。

新增 Caddyfile.dmit 与 docker-compose-aicodex.yml 部署配置，
用于宿主机场景下的反向代理与服务编排。

Co-Authored-By: Claude Opus 4.6 <noreply@anthropic.com>

backend/internal/service/openai_ws_forwarder.go

@@ -46,9 +46,10 @@ const (
 	openAIWSPayloadSizeEstimateMaxBytes = 64 * 1024
 	openAIWSPayloadSizeEstimateMaxItems = 16
 
-	openAIWSEventFlushBatchSizeDefault = 4
-	openAIWSEventFlushIntervalDefault  = 25 * time.Millisecond
-	openAIWSPayloadLogSampleDefault    = 0.2
+	openAIWSEventFlushBatchSizeDefault    = 4
+	openAIWSEventFlushIntervalDefault     = 25 * time.Millisecond
+	openAIWSPayloadLogSampleDefault       = 0.2
+	openAIWSPassthroughIdleTimeoutDefault = time.Hour
 
 	openAIWSStoreDisabledConnModeStrict   = "strict"
 	openAIWSStoreDisabledConnModeAdaptive = "adaptive"
@@ -904,6 +905,18 @@ func (s *OpenAIGatewayService) getOpenAIWSConnPool() *openAIWSConnPool {
 	return s.openaiWSPool
 }
 
+func (s *OpenAIGatewayService) getOpenAIWSPassthroughDialer() openAIWSClientDialer {
+	if s == nil {
+		return nil
+	}
+	s.openaiWSPassthroughDialerOnce.Do(func() {
+		if s.openaiWSPassthroughDialer == nil {
+			s.openaiWSPassthroughDialer = newDefaultOpenAIWSClientDialer()
+		}
+	})
+	return s.openaiWSPassthroughDialer
+}
+
 func (s *OpenAIGatewayService) SnapshotOpenAIWSPoolMetrics() OpenAIWSPoolMetricsSnapshot {
 	pool := s.getOpenAIWSConnPool()
 	if pool == nil {
@@ -967,6 +980,13 @@ func (s *OpenAIGatewayService) openAIWSReadTimeout() time.Duration {
 	return 15 * time.Minute
 }
 
+func (s *OpenAIGatewayService) openAIWSPassthroughIdleTimeout() time.Duration {
+	if timeout := s.openAIWSReadTimeout(); timeout > 0 {
+		return timeout
+	}
+	return openAIWSPassthroughIdleTimeoutDefault
+}
+
 func (s *OpenAIGatewayService) openAIWSWriteTimeout() time.Duration {
 	if s != nil && s.cfg != nil && s.cfg.Gateway.OpenAIWS.WriteTimeoutSeconds > 0 {
 		return time.Duration(s.cfg.Gateway.OpenAIWS.WriteTimeoutSeconds) * time.Second
@@ -2322,7 +2342,7 @@ func (s *OpenAIGatewayService) ProxyResponsesWebSocketFromClient(
 
 	wsDecision := s.getOpenAIWSProtocolResolver().Resolve(account)
 	modeRouterV2Enabled := s != nil && s.cfg != nil && s.cfg.Gateway.OpenAIWS.ModeRouterV2Enabled
-	ingressMode := OpenAIWSIngressModeShared
+	ingressMode := OpenAIWSIngressModeCtxPool
 	if modeRouterV2Enabled {
 		ingressMode = account.ResolveOpenAIResponsesWebSocketV2Mode(s.cfg.Gateway.OpenAIWS.IngressModeDefault)
 		if ingressMode == OpenAIWSIngressModeOff {
@@ -2332,6 +2352,30 @@ func (s *OpenAIGatewayService) ProxyResponsesWebSocketFromClient(
 				nil,
 			)
 		}
+		switch ingressMode {
+		case OpenAIWSIngressModePassthrough:
+			if wsDecision.Transport != OpenAIUpstreamTransportResponsesWebsocketV2 {
+				return fmt.Errorf("websocket ingress requires ws_v2 transport, got=%s", wsDecision.Transport)
+			}
+			return s.proxyResponsesWebSocketV2Passthrough(
+				ctx,
+				c,
+				clientConn,
+				account,
+				token,
+				firstClientMessage,
+				hooks,
+				wsDecision,
+			)
+		case OpenAIWSIngressModeCtxPool, OpenAIWSIngressModeShared, OpenAIWSIngressModeDedicated:
+			// continue
+		default:
+			return NewOpenAIWSClientCloseError(
+				coderws.StatusPolicyViolation,
+				"websocket mode only supports ctx_pool/passthrough",
+				nil,
+			)
+		}
 	}
 	if wsDecision.Transport != OpenAIUpstreamTransportResponsesWebsocketV2 {
 		return fmt.Errorf("websocket ingress requires ws_v2 transport, got=%s", wsDecision.Transport)