feat(usage): 用量记录落库上游请求标识并支持按账户配置响应头名

- usage_logs 新增 upstream_request_id 列（迁移 232）与仅索引非空行的 CONCURRENTLY 部分索引（迁移 233，runner 登记失效索引清理）
- 账户 extra.upstream_request_id_header 指定要读取的上游响应头，只读该头；留空不记录；创建/更新/批量入口校验头名合法且不超过 64 字节
- ForwardResult/OpenAIForwardResult 携带 UpstreamHeaders，中央计费按账户解析落库，WS 轮次保持 NULL
- 管理端用量明细新增默认隐藏的"上游ID"列，带与请求ID列一致的复制按钮，并同步导出
- 创建/编辑账户弹窗新增"上游ID"输入（UpstreamRequestIdHeaderField），提示按接入类型与平台分条列出常见头名
- HelpTooltip 悬停模式下指针移入提示框时保持打开，便于选中复制提示内容

backend/internal/handler/admin/account_handler.go

@@ -837,6 +837,10 @@ func (h *AccountHandler) Create(c *gin.Context) {
 	}
 	// base_rpm 输入校验：负值归零，超过 10000 截断
 	sanitizeExtraBaseRPM(req.Extra)
+	if err := service.ValidateUpstreamRequestIDHeaderExtra(req.Extra); err != nil {
+		response.ErrorFrom(c, err)
+		return
+	}
 
 	// 确定是否跳过混合渠道检查
 	skipCheck := req.ConfirmMixedChannelRisk != nil && *req.ConfirmMixedChannelRisk
@@ -970,6 +974,10 @@ func (h *AccountHandler) Update(c *gin.Context) {
 	}
 	// base_rpm 输入校验：负值归零，超过 10000 截断
 	sanitizeExtraBaseRPM(req.Extra)
+	if err := service.ValidateUpstreamRequestIDHeaderExtra(req.Extra); err != nil {
+		response.ErrorFrom(c, err)
+		return
+	}
 
 	// 确定是否跳过混合渠道检查
 	skipCheck := req.ConfirmMixedChannelRisk != nil && *req.ConfirmMixedChannelRisk
@@ -1424,6 +1432,10 @@ func (h *AccountHandler) ApplyOAuthCredentials(c *gin.Context) {
 		response.ErrorFrom(c, err)
 		return
 	}
+	if err := service.ValidateUpstreamRequestIDHeaderExtra(req.Extra); err != nil {
+		response.ErrorFrom(c, err)
+		return
+	}
 
 	// Drop SSO/password residue; re-auth must leave only OAuth tokens on disk.
 	req.Credentials = service.SanitizeStoredCredentials(existing.Platform, req.Credentials)
@@ -1897,6 +1909,15 @@ func (h *AccountHandler) BatchCreate(c *gin.Context) {
 
 			// base_rpm 输入校验：负值归零，超过 10000 截断
 			sanitizeExtraBaseRPM(item.Extra)
+			if err := service.ValidateUpstreamRequestIDHeaderExtra(item.Extra); err != nil {
+				failed++
+				results = append(results, gin.H{
+					"name":    item.Name,
+					"success": false,
+					"error":   err.Error(),
+				})
+				continue
+			}
 
 			skipCheck := item.ConfirmMixedChannelRisk != nil && *item.ConfirmMixedChannelRisk
 
@@ -2091,6 +2112,10 @@ func (h *AccountHandler) BulkUpdate(c *gin.Context) {
 	}
 	// base_rpm 输入校验：负值归零，超过 10000 截断
 	sanitizeExtraBaseRPM(req.Extra)
+	if err := service.ValidateUpstreamRequestIDHeaderExtra(req.Extra); err != nil {
+		response.ErrorFrom(c, err)
+		return
+	}
 
 	// 确定是否跳过混合渠道检查
 	skipCheck := req.ConfirmMixedChannelRisk != nil && *req.ConfirmMixedChannelRisk

backend/internal/handler/dto/mappers.go

@@ -723,6 +723,7 @@ func UsageLogFromServiceAdmin(l *service.UsageLog) *AdminUsageLog {
 		UpstreamModelMismatch:   l.UpstreamModelMismatch,
 		ChannelID:               l.ChannelID,
 		ModelMappingChain:       l.ModelMappingChain,
+		UpstreamRequestID:       l.UpstreamRequestID,
 		BillingTier:             l.BillingTier,
 		AccountRateMultiplier:   l.AccountRateMultiplier,
 		AccountStatsCost:        l.AccountStatsCost,

backend/internal/handler/dto/types.go

@@ -588,6 +588,8 @@ type AdminUsageLog struct {
 	ChannelID *int64 `json:"channel_id,omitempty"`
 	// ModelMappingChain 模型映射链，如 "a→b→c"
 	ModelMappingChain *string `json:"model_mapping_chain,omitempty"`
+	// UpstreamRequestID 是直接上游声明的请求标识，仅管理端可见。
+	UpstreamRequestID *string `json:"upstream_request_id,omitempty"`
 	// BillingTier 计费层级标签（per_request/image 模式）
 	BillingTier *string `json:"billing_tier,omitempty"`