fix: improve foreground notification

[jvsena42]

Fixes #651
Fixes #658

This PR fixes multiple issues with the foreground notification in LightningNodeService:

Description

1. Makes the notification non-dismissable by adding .setOngoing(true)
2. Handles Android 15+ foreground service timeout by implementing onTimeout() callback
3. Improves the notification icon and adds brand color for better visibility
4. Removes redundant duplicate startForeground() call

Preview

api-level-36.webm

api-level-33.webm

QA Notes

1. Non-dismissable notification

1. Open the app with a configured wallet
2. Pull down the notification shade
3. Try to swipe away the "Bitkit is running" notification
4. Node: on API level 33+ (android 13) it is possible to hide ongoing notifications, see preview

2. Notification appearance

1. Check the notification in the notification shade
2. Verify: Icon is recognizable with brand orange color (#FF4400)

3. Android 15+ timeout handling (optional)

To test the FGS timeout on Android 15 (not above):

adb shell am compat enable FGS_INTRODUCE_TIME_LIMITS to.bitkit
adb shell device_config put activity_manager data_sync_fgs_timeout_duration 60000

Wait 60 seconds and verify the service stops gracefully without crash.

[claude]

Code review

No issues found. Checked for bugs and CLAUDE.md compliance.

[jvsena42]

Still not tested the adb commands