fix(time): handle Sunday correctly in TimeWeekStart

On Sunday, Weekday() returns 0, causing (0-1)*-24 = +24 hours which
jumped forward to next Monday instead of back to last Monday. This
affected any weekly reset logic running on Sundays.

server/channelserver/sys_time.go

@@ -16,7 +16,11 @@ func TimeMidnight() time.Time {
 
 func TimeWeekStart() time.Time {
 	midnight := TimeMidnight()
-	offset := (int(midnight.Weekday()) - 1) * -24
+	weekday := int(midnight.Weekday())
+	if weekday == 0 {
+		weekday = 7 // Treat Sunday as day 7
+	}
+	offset := (weekday - 1) * -24
 	return midnight.Add(time.Hour * time.Duration(offset))
 }