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_group_reset_test.go

@@ -0,0 +1,127 @@
+package service
+
+import (
+	"testing"
+
+	"github.com/mhsanaei/3x-ui/v3/internal/database"
+	"github.com/mhsanaei/3x-ui/v3/internal/database/model"
+	"github.com/mhsanaei/3x-ui/v3/internal/xray"
+)
+
+func groupByName(t *testing.T, svc *ClientService, name string) GroupSummary {
+	t.Helper()
+	rows, err := svc.ListGroups()
+	if err != nil {
+		t.Fatalf("ListGroups: %v", err)
+	}
+	for _, g := range rows {
+		if g.Name == name {
+			return g
+		}
+	}
+	t.Fatalf("group %q not found in %v", name, rows)
+	return GroupSummary{}
+}
+
+func seedGroupedClient(t *testing.T, email, group string, up, down int64) {
+	t.Helper()
+	if err := database.GetDB().Create(&model.ClientRecord{Email: email, Enable: true, Group: group}).Error; err != nil {
+		t.Fatalf("seed client record %q: %v", email, err)
+	}
+	seedClientRow(t, email, 1, up, down, 0)
+}
+
+func TestResetGroupTraffic_ZeroesGroupButKeepsClients(t *testing.T) {
+	initTrafficTestDB(t)
+	svc := &ClientService{}
+
+	seedGroupedClient(t, "alice", "vip", 100, 200)
+	seedGroupedClient(t, "bob", "vip", 50, 50)
+
+	before := groupByName(t, svc, "vip")
+	if before.Up != 150 || before.Down != 250 || before.TrafficUsed != 400 || before.ClientCount != 2 {
+		t.Fatalf("before reset: got %+v, want up=150 down=250 used=400 count=2", before)
+	}
+
+	if err := svc.ResetGroupTraffic("vip"); err != nil {
+		t.Fatalf("ResetGroupTraffic: %v", err)
+	}
+
+	after := groupByName(t, svc, "vip")
+	if after.Up != 0 || after.Down != 0 || after.TrafficUsed != 0 {
+		t.Fatalf("after reset: got %+v, want up=0 down=0 used=0", after)
+	}
+	if after.ClientCount != 2 {
+		t.Fatalf("after reset: client count changed to %d, want 2", after.ClientCount)
+	}
+
+	var alice xray.ClientTraffic
+	if err := database.GetDB().Where("email = ?", "alice").First(&alice).Error; err != nil {
+		t.Fatalf("load alice traffic: %v", err)
+	}
+	if alice.Up != 100 || alice.Down != 200 {
+		t.Fatalf("client counter modified by group reset: alice up=%d down=%d, want 100/200", alice.Up, alice.Down)
+	}
+}
+
+func TestResetGroupTraffic_NewTrafficAccumulatesAboveBaseline(t *testing.T) {
+	initTrafficTestDB(t)
+	svc := &ClientService{}
+
+	seedGroupedClient(t, "carol", "team", 100, 100)
+	if err := svc.ResetGroupTraffic("team"); err != nil {
+		t.Fatalf("ResetGroupTraffic: %v", err)
+	}
+	if g := groupByName(t, svc, "team"); g.Up != 0 || g.Down != 0 {
+		t.Fatalf("after reset: got %+v, want up=0 down=0", g)
+	}
+
+	if err := database.GetDB().Table("client_traffics").
+		Where("email = ?", "carol").
+		Updates(map[string]any{"up": 130, "down": 100}).Error; err != nil {
+		t.Fatalf("bump carol traffic: %v", err)
+	}
+
+	g := groupByName(t, svc, "team")
+	if g.Up != 30 || g.Down != 0 || g.TrafficUsed != 30 {
+		t.Fatalf("post-bump: got %+v, want up=30 down=0 used=30", g)
+	}
+}
+
+func TestResetGroupTraffic_CreatesRowForDerivedGroup(t *testing.T) {
+	initTrafficTestDB(t)
+	svc := &ClientService{}
+
+	seedGroupedClient(t, "dave", "adhoc", 70, 30)
+
+	var rows int64
+	if err := database.GetDB().Model(&model.ClientGroup{}).Where("name = ?", "adhoc").Count(&rows).Error; err != nil {
+		t.Fatalf("count client_groups: %v", err)
+	}
+	if rows != 0 {
+		t.Fatalf("precondition: derived group should have no client_groups row, got %d", rows)
+	}
+
+	if err := svc.ResetGroupTraffic("adhoc"); err != nil {
+		t.Fatalf("ResetGroupTraffic: %v", err)
+	}
+
+	var stored model.ClientGroup
+	if err := database.GetDB().Where("name = ?", "adhoc").First(&stored).Error; err != nil {
+		t.Fatalf("client_groups row not created: %v", err)
+	}
+	if stored.ResetUp != 70 || stored.ResetDown != 30 {
+		t.Fatalf("baseline not snapshotted: got up=%d down=%d, want 70/30", stored.ResetUp, stored.ResetDown)
+	}
+	if g := groupByName(t, svc, "adhoc"); g.Up != 0 || g.Down != 0 {
+		t.Fatalf("after reset: got %+v, want up=0 down=0", g)
+	}
+}
+
+func TestResetGroupTraffic_EmptyNameRejected(t *testing.T) {
+	initTrafficTestDB(t)
+	svc := &ClientService{}
+	if err := svc.ResetGroupTraffic("   "); err == nil {
+		t.Fatal("ResetGroupTraffic(blank) = nil, want error")
+	}
+}