feat(groups): reset group traffic without touching client counters

The group page shows traffic counting per group, but the only reset
available zeroed every member client's up/down counters (and their
quotas) via bulkResetTraffic. Group traffic is a derived sum of client
traffic, so zeroing the group display previously required mutating the
clients themselves.

Add a display-only baseline: ClientGroup gains reset_up/reset_down
columns (additive, handled by AutoMigrate). ResetGroupTraffic snapshots
the group's current up/down sum into the baseline, and ListGroups now
reports max(0, sum - baseline). Client counters are left untouched and
no Xray restart is triggered. A new POST /panel/api/clients/groups/
resetTraffic endpoint drives it, creating the client_groups row when the
group exists only as a derived label.

The groups page action now calls the new endpoint; confirm/success
strings updated across all 13 locales to reflect group-only semantics.

internal/web/service/client_groups.go

@@ -36,21 +36,32 @@ func (s *ClientService) ListGroups() ([]GroupSummary, error) {
 		return nil, err
 	}
 	type groupAgg struct {
-		count   int
-		traffic int64
-		up      int64
-		down    int64
+		count int
+		up    int64
+		down  int64
 	}
+	baseUp := make(map[string]int64, len(stored))
+	baseDown := make(map[string]int64, len(stored))
 	merged := make(map[string]groupAgg, len(derived)+len(stored))
 	for _, g := range stored {
 		merged[g.Name] = groupAgg{}
+		baseUp[g.Name] = g.ResetUp
+		baseDown[g.Name] = g.ResetDown
 	}
 	for _, g := range derived {
-		merged[g.Name] = groupAgg{count: g.ClientCount, traffic: g.TrafficUsed, up: g.Up, down: g.Down}
+		merged[g.Name] = groupAgg{count: g.ClientCount, up: g.Up, down: g.Down}
 	}
 	out := make([]GroupSummary, 0, len(merged))
 	for name, agg := range merged {
-		out = append(out, GroupSummary{Name: name, ClientCount: agg.count, TrafficUsed: agg.traffic, Up: agg.up, Down: agg.down})
+		up := agg.up - baseUp[name]
+		if up < 0 {
+			up = 0
+		}
+		down := agg.down - baseDown[name]
+		if down < 0 {
+			down = 0
+		}
+		out = append(out, GroupSummary{Name: name, ClientCount: agg.count, TrafficUsed: up + down, Up: up, Down: down})
 	}
 	sort.Slice(out, func(i, j int) bool {
 		return strings.ToLower(out[i].Name) < strings.ToLower(out[j].Name)
@@ -77,6 +88,34 @@ func (s *ClientService) EmailsByGroup(name string) ([]string, error) {
 	return emails, nil
 }
 
+func (s *ClientService) ResetGroupTraffic(name string) error {
+	name = strings.TrimSpace(name)
+	if name == "" {
+		return common.NewError("group name is required")
+	}
+	db := database.GetDB()
+	var agg struct {
+		Up   int64
+		Down int64
+	}
+	if err := db.Table("clients AS c").
+		Select("COALESCE(SUM(ct.up), 0) AS up, COALESCE(SUM(ct.down), 0) AS down").
+		Joins("LEFT JOIN client_traffics ct ON ct.email = c.email").
+		Where("c.group_name = ?", name).
+		Scan(&agg).Error; err != nil {
+		return err
+	}
+	var count int64
+	if err := db.Model(&model.ClientGroup{}).Where("name = ?", name).Count(&count).Error; err != nil {
+		return err
+	}
+	if count == 0 {
+		return db.Create(&model.ClientGroup{Name: name, ResetUp: agg.Up, ResetDown: agg.Down}).Error
+	}
+	return db.Model(&model.ClientGroup{}).Where("name = ?", name).
+		Updates(map[string]any{"reset_up": agg.Up, "reset_down": agg.Down}).Error
+}
+
 func (s *ClientService) CreateGroup(name string) error {
 	name = strings.TrimSpace(name)
 	if name == "" {