fix(service): prevent notification flickering when auto-tunnel is active

[naonak]

Summary

Fix two issues causing the "Tunnel running" notification (ID 100) to flicker visually when auto-tunnel is active (I have Android 16).

Problem

When both the VPN notification (ID 100) and the auto-tunnel notification (ID 122) are visible in the notification shade simultaneously:

1. Race condition on service lifecycle: onDestroy() in AutoTunnelService and BaseTunnelForegroundService called STOP_FOREGROUND_REMOVE, which globally cancels the notification ID. During a rapid stop/start cycle (e.g. network transition), this could remove a notification already posted by the newly started service instance, causing Android 16 to kill the foreground service that lost its notification.

2. Notification drawer flicker: The statsJob updated the VPN notification every second via NotificationManager.notify(). Each update triggers a full re-layout of the notification shade. With two stacked notifications from the same app, this causes both to visually jump every second.

Solution

• Changed onDestroy() in both services to use STOP_FOREGROUND_DETACH instead of STOP_FOREGROUND_REMOVE. The intentional stop path (stop()) still uses STOP_FOREGROUND_REMOVE before stopSelf() to cleanly remove the notification.
• Switched statsJob from NotificationManager.notify() to ServiceCompat.startForeground() (correct API for updating a foreground service notification).
• Only update the notification when traffic stats actually change (skip re-layouts during idle periods).
• Reduced the stats poll interval from 1s to 5s.

Technical Design

Files changed:

• AutoTunnelService.kt: Added STOP_FOREGROUND_REMOVE in stop() before stopSelf(); changed onDestroy() to STOP_FOREGROUND_DETACH.
• BaseTunnelForegroundService.kt: Changed onDestroy() to STOP_FOREGROUND_DETACH; refactored statsJob to use startForeground(), conditional updates, and 5s interval.

Before / After (statsJob):

// Before
notificationManager.show(VPN_NOTIFICATION_ID, notification)
delay(1000)

// After
var lastTraffic: Pair<Long, Long>? = null
if (traffic != lastTraffic) {
    lastTraffic = traffic
    ServiceCompat.startForeground(this@..., VPN_NOTIFICATION_ID, notification, fgsType)
}
delay(5000)

Test Plan

• Auto-tunnel active + tunnel running → both notifications visible → no flickering at rest
• Active traffic → notification updates at most every 5s, no jarring jump
• Tunnel idle (no traffic) → zero notification updates
• Disable auto-tunnel → VPN notification disappears cleanly
• Network transition with auto-tunnel → stop/start cycle completes without leaving a stale notification