feat(sub): add opt-in month-end expiry presentation (#6517)

Offer monthly calendar subscriptions an explicit last-valid-second display
without moving their real billing boundary or spending renewal allowances.

Keep the option off by default and limit conversion to a shared fixed
day-1 midnight cutoff at an actual month transition in the panel timezone.
Use the authoritative client calendar mode when aggregating node traffic,
and share the header formatter across raw, JSON, and Clash exports.

Expose the setting in the existing settings API/UI, regenerate its schemas,
and document that clients may report expiry one second early or format the
date differently in another timezone. Add HTTP, settings, and DST coverage.
Stored deadlines, access enforcement, info/remark expiry values, and renewal
accounting remain unchanged.

Refs: #6516

Co-authored-by: JacktheRanger <219502738+JacktheRanger@users.noreply.github.com>

internal/sub/service.go

@@ -48,6 +48,8 @@ type SubService struct {
 	usageShown                 map[string]bool
 	showIdentityOnAllLinks     bool
 	subInfoNodeEnable          bool
+	subCalendarExpireInclusive bool
+	calendarExpireLocation     *time.Location
 	subExpiredTemplate         string
 	subTrafficDepletedTemplate string
 	inboundService             service.InboundService
@@ -111,6 +113,11 @@ func (s *SubService) PrepareForRequest(host string) {
 	s.settingsByInbound = map[int]map[string]any{}
 	s.loadNodes()
 	s.loadRemarkSettings()
+	s.subCalendarExpireInclusive, _ = s.settingService.GetSubCalendarExpireInclusive()
+	s.calendarExpireLocation = nil
+	if s.subCalendarExpireInclusive {
+		s.calendarExpireLocation, _ = s.settingService.GetTimeLocation()
+	}
 }
 
 // primeLinkClients caches clients (first occurrence per email, matching the
@@ -544,13 +551,13 @@ func (s *SubService) AggregateTrafficByEmails(emails []string) (xray.ClientTraff
 	// runtime traffic rows. In a multi-node setup the node snapshot can reset
 	// client_traffics.total/expiry_time to 0, so fall back to the clients
 	// table to keep the Subscription-Userinfo header in sync with the UI (#4645).
-	limits := make(map[string][2]int64, len(emails))
+	limits := make(map[string]model.ClientRecord, len(emails))
 	var records []model.ClientRecord
 	if err := db.Model(&model.ClientRecord{}).Where("email IN ?", emails).Find(&records).Error; err != nil {
 		logger.Warning("SubService - AggregateTrafficByEmails: load client limits:", err)
 	} else {
 		for _, r := range records {
-			limits[r.Email] = [2]int64{r.TotalGB, r.ExpiryTime}
+			limits[r.Email] = r
 		}
 	}
 
@@ -560,25 +567,33 @@ func (s *SubService) AggregateTrafficByEmails(emails []string) (xray.ClientTraff
 		if ct.LastOnline > lastOnline {
 			lastOnline = ct.LastOnline
 		}
-		total, expiry := ct.Total, ct.ExpiryTime
+		total, expiry, resetDay := ct.Total, ct.ExpiryTime, ct.ResetDay
 		if lim, ok := limits[ct.Email]; ok {
+			resetDay = lim.ResetDay
 			if total == 0 {
-				total = lim[0]
+				total = lim.TotalGB
 			}
 			if expiry == 0 {
-				expiry = lim[1]
+				expiry = lim.ExpiryTime
 			}
 		}
+		if expiry <= 0 {
+			resetDay = 0
+		}
 		if first {
 			agg.Up = ct.Up
 			agg.Down = ct.Down
 			agg.Total = total
 			agg.ExpiryTime = subscriptionExpiryFromClient(now, expiry)
+			agg.ResetDay = resetDay
 			first = false
 			continue
 		}
 		agg.Up += ct.Up
 		agg.Down += ct.Down
+		if resetDay != agg.ResetDay {
+			agg.ResetDay = 0
+		}
 		if agg.Total == 0 || total == 0 {
 			agg.Total = 0
 		} else {