fix(grok): 移除 Chat Completions 中不支持的 external_web_access 参数

模型：Claude Sonnet 5
修复内容：在 Grok Chat Completions raw 转发流程中添加 external_web_access 参数过滤，修复 Grok API 返回 400 "Argument not supported: external_web_access" 错误
修改理由：Grok xAI API 不支持 external_web_access 参数，Sub2API Responses API 路径已有过滤，但 Chat Completions 路径缺失，导致 grok-4.5 等模型调用失败返回 502
验证结果：代码已通过本地 Demo 验证递归删除逻辑正常，待远端编译部署后验证真实 API 调用
影响范围：仅影响 Grok 平台 Chat Completions API 请求体处理，不影响 Responses API 和其他平台
回滚方式：git revert 本次提交，或手动移除 openai_gateway_chat_completions_raw.go line 159-163 的 sanitizeGrokUnsupportedFields 调用

[AI: 梁心语/Claude Sonnet 5 @ 2026-09-08T17:30]

backend/internal/service/openai_gateway_chat_completions_raw.go

@@ -156,6 +156,10 @@ func (s *OpenAIGatewayService) forwardAsRawChatCompletions(
 		if err != nil {
 			return nil, fmt.Errorf("normalize Grok chat reasoning effort: %w", err)
 		}
+		upstreamBody, err = sanitizeGrokUnsupportedFields(upstreamBody)
+		if err != nil {
+			return nil, fmt.Errorf("sanitize Grok unsupported fields: %w", err)
+		}
 	}
 	upstreamBody = applyOllamaCloudRawChatCompletionsRequest(account, upstreamBody)
 

backend/internal/service/openai_gateway_grok.go

@@ -752,11 +752,14 @@ func grokSupportsReasoningEffort(model string) bool {
 	}
 }
 
-var grokResponsesUnsupportedRecursiveFields = map[string]struct{}{
+// grokUnsupportedRecursiveFields 定义 Grok 平台（Responses 和 Chat Completions）不支持的字段
+var grokUnsupportedRecursiveFields = map[string]struct{}{
 	"external_web_access": {},
 }
 
-func sanitizeGrokResponsesUnsupportedFields(body []byte) ([]byte, error) {
+// sanitizeGrokUnsupportedFields 递归移除 Grok 平台不支持的字段
+// 适用于 Responses API 和 Chat Completions API
+func sanitizeGrokUnsupportedFields(body []byte) ([]byte, error) {
 	if !bytes.Contains(body, []byte(`"external_web_access"`)) {
 		return body, nil
 	}
@@ -765,12 +768,15 @@ func sanitizeGrokResponsesUnsupportedFields(body []byte) ([]byte, error) {
 	if err := decodeOpenAIJSONUseNumber(body, &payload); err != nil {
 		return nil, err
 	}
-	if !deleteJSONFields(payload, grokResponsesUnsupportedRecursiveFields) {
+	if !deleteJSONFields(payload, grokUnsupportedRecursiveFields) {
 		return body, nil
 	}
 	return marshalOpenAIUpstreamJSON(payload)
 }
 
+// sanitizeGrokResponsesUnsupportedFields 保留旧函数名作为别名，向后兼容
+var sanitizeGrokResponsesUnsupportedFields = sanitizeGrokUnsupportedFields
+
 func deleteJSONFields(value any, fields map[string]struct{}) bool {
 	switch typed := value.(type) {
 	case map[string]any: