fix(openai): handle codex spark model limitations

backend/internal/service/openai_gateway_service.go

@@ -1995,6 +1995,17 @@ func (s *OpenAIGatewayService) Forward(ctx context.Context, c *gin.Context, acco
 			account.Type,
 		)
 	}
+	if err := validateCodexSparkInput(reqBody, upstreamModel); err != nil {
+		setOpsUpstreamError(c, http.StatusBadRequest, err.Error(), "")
+		c.JSON(http.StatusBadRequest, gin.H{
+			"error": gin.H{
+				"type":    "invalid_request_error",
+				"message": err.Error(),
+				"param":   "input",
+			},
+		})
+		return nil, err
+	}
 
 	// OpenAI OAuth 账号走 ChatGPT internal Codex endpoint，需要将模型名规范化为
 	// 上游可识别的 Codex/GPT 系列。API Key 账号则应保留原始/映射后的模型名，