* fix: prevent online clients from randomly disappearing from panel UI
Online status was determined solely by whether a client transferred
bytes in the current 5-second polling window. The online list was
completely replaced each cycle, so idle-but-connected clients with no
traffic delta in that window were dropped from the UI.
Now online status is computed from lastOnline DB timestamps with a
5-second grace period via RefreshOnlineClientsFromMap(), so clients
remain visible across idle polling windows.
Closes#4384
* fix: extend online client grace period to survive idle poll cycles
The 5s grace period equalled the traffic-poll interval, so a client
whose Xray stats reported a zero delta for one cycle was still dropped
on the very next tick. Bump to 20s (~4 polls) so idle-but-connected
sessions stay visible across momentary counter gaps without lingering
long after a real disconnect.
Refs #4384
---------
Co-authored-by: MHSanaei <ho3ein.sanaei@gmail.com>
78f1719c6d