fix(openai): log /v1/chat/completions upstream endpoint for chat-only API-key accounts

DeriveUpstreamEndpoint maps every OpenAI-platform request to /v1/responses, but
API-key accounts whose upstream only speaks Chat Completions
(!ShouldUseResponsesAPI) are forwarded directly to /v1/chat/completions. The
messages, responses and cyber-policy recording sites derived the endpoint via the
bare GetUpstreamEndpoint, so usage/ops records mislabeled those requests as
/v1/responses. Generalize the existing resolveRawCCUpstreamEndpoint into
resolveOpenAIUpstreamEndpoint and use it at every OpenAI recording site, matching
the already-correct chat-completions client path.

backend/internal/handler/openai_gateway_handler.go

@@ -496,7 +496,7 @@ func (h *OpenAIGatewayHandler) Responses(c *gin.Context) {
 		clientIP := ip.GetClientIP(c)
 		requestPayloadHash := service.HashUsageRequestPayload(body)
 		inboundEndpoint := GetInboundEndpoint(c)
-		upstreamEndpoint := GetUpstreamEndpoint(c, account.Platform)
+		upstreamEndpoint := resolveOpenAIUpstreamEndpoint(c, account)
 
 		// 使用量记录通过有界 worker 池提交，避免请求热路径创建无界 goroutine。
 		cyberBlocked := service.GetOpsCyberPolicy(c) != nil
@@ -901,7 +901,7 @@ func (h *OpenAIGatewayHandler) Messages(c *gin.Context) {
 		clientIP := ip.GetClientIP(c)
 		requestPayloadHash := service.HashUsageRequestPayload(body)
 		inboundEndpoint := GetInboundEndpoint(c)
-		upstreamEndpoint := GetUpstreamEndpoint(c, account.Platform)
+		upstreamEndpoint := resolveOpenAIUpstreamEndpoint(c, account)
 
 		cyberBlocked := service.GetOpsCyberPolicy(c) != nil
 		h.submitOpenAIUsageRecordTask(c.Request.Context(), result, func(ctx context.Context) {
@@ -1496,7 +1496,7 @@ func (h *OpenAIGatewayHandler) ResponsesWebSocket(c *gin.Context) {
 				}
 				h.gatewayService.ReportOpenAIAccountScheduleResult(account.ID, true, result.FirstTokenMs)
 				inboundEndpoint := GetInboundEndpoint(c)
-				upstreamEndpoint := GetUpstreamEndpoint(c, account.Platform)
+				upstreamEndpoint := resolveOpenAIUpstreamEndpoint(c, account)
 				cyberBlocked := service.GetOpsCyberPolicy(c) != nil
 				h.submitOpenAIUsageRecordTask(ctx, result, func(taskCtx context.Context) {
 					if err := h.gatewayService.RecordUsage(taskCtx, &service.OpenAIRecordUsageInput{
@@ -2297,7 +2297,7 @@ func (h *OpenAIGatewayHandler) recordCyberPolicyIfMarked(c *gin.Context, apiKey
 	var accountID int64
 	if account != nil {
 		accountID = account.ID
-		upstreamEndpoint = GetUpstreamEndpoint(c, account.Platform)
+		upstreamEndpoint = resolveOpenAIUpstreamEndpoint(c, account)
 	}
 	stream := false
 	if v, ok := c.Get(opsStreamKey); ok {