Upgrade turn notifications: new v2 channel, higher importance, icons, and defaults

[siddheshkothadi]

Motivation

• Make turn-completed notifications more prominent and avoid users keeping muted settings by using a new channel ID turn_events_v2 so channel defaults are reapplied.
• Improve visibility and feedback for important events by increasing importance and enabling vibration/lights.
• Provide a richer visual notification using the app icon as a large icon and a modern small icon resource.

Description

• Renamed TURN_CHANNEL_ID to turn_events_v2 to force a fresh notification channel with updated defaults.
• Created the channel with NotificationManager.IMPORTANCE_HIGH, enabled vibration and lights, and kept badges via setShowBadge(true).
• Updated notification builder to use R.drawable.ic_launcher_foreground as the small icon, attempt to load the app icon as a large icon using toBitmap, set priority to PRIORITY_HIGH, and apply .setDefaults(NotificationCompat.DEFAULT_ALL).
• Added import for toBitmap and wrapped large icon extraction with runCatching to safely handle failures.

Testing

• No automated tests were run as part of this change.

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Codex Task