feat(dashboard): add admin user analytics and fix chart labels

- Add GET /api/data/users endpoint for user-grouped quota data (admin only)
- Add user consumption ranking (horizontal bar, top 10) and user consumption
  trend (area chart) tabs visible only to admin users
- Fix mislabeled "消耗趋势" tab to "调用趋势" (shows call counts, not quota)
- Add processUserData helper for user ranking and trend data extraction
- Add i18n keys for new tabs across all 7 locales

model/usedata.go

@@ -115,6 +115,16 @@ func GetQuotaDataByUserId(userId int, startTime int64, endTime int64) (quotaData
 	return quotaDatas, err
 }
 
+func GetQuotaDataGroupByUser(startTime int64, endTime int64) (quotaData []*QuotaData, err error) {
+	var quotaDatas []*QuotaData
+	err = DB.Table("quota_data").
+		Select("username, created_at, sum(count) as count, sum(quota) as quota, sum(token_used) as token_used").
+		Where("created_at >= ? and created_at <= ?", startTime, endTime).
+		Group("username, created_at").
+		Find(&quotaDatas).Error
+	return quotaDatas, err
+}
+
 func GetAllQuotaDates(startTime int64, endTime int64, username string) (quotaData []*QuotaData, err error) {
 	if username != "" {
 		return GetQuotaDataByUsername(username, startTime, endTime)