Develop - Critical bug fix with batteries notification

[sameerasw]

This pull request improves the handling of the battery notification service to ensure a persistent foreground notification is always shown, even when no battery devices are connected. It also introduces a new user-facing message for this scenario and updates the app version.

Battery Notification Service Improvements:

• Ensured that the BatteryNotificationService always starts in the foreground with a notification, both on onCreate and onStartCommand, to comply with Android background execution limits and prevent the service from being killed.
• Refactored notification logic so that when no battery devices are connected, a persistent notification is shown with a "No devices connected" message, instead of stopping the service.
• Added a new buildBaseNotification helper method to standardize notification creation for both empty and non-empty battery device states.

User Interface:

• Added a new string resource battery_notification_no_devices to display a clear message when there are no connected devices.

App Versioning:

• Bumped versionCode to 28 and versionName to "11.4" in app/build.gradle.kts to reflect the new release.