Merge upstream/main into pr/upstream-model-tracking

Ultraworked with [Sisyphus](https://github.com/code-yeongyu/oh-my-openagent)

Co-authored-by: Sisyphus <clio-agent@sisyphuslabs.ai>

backend/internal/pkg/usagestats/usage_log_types.go

@@ -112,6 +112,13 @@ type EndpointStat struct {
 	ActualCost  float64 `json:"actual_cost"` // 实际扣除
 }
 
+// GroupUsageSummary represents today's and cumulative cost for a single group.
+type GroupUsageSummary struct {
+	GroupID   int64   `json:"group_id"`
+	TodayCost float64 `json:"today_cost"`
+	TotalCost float64 `json:"total_cost"`
+}
+
 // GroupStat represents usage statistics for a single group
 type GroupStat struct {
 	GroupID     int64   `json:"group_id"`