General: Add Bluetooth connection status icon to toolbar

[d4rken]

What changed

Added a dynamic Bluetooth status icon to the overview toolbar that shows the current connection state at a glance and links to Android Bluetooth settings.

• Icon is hidden until you have a device profile and Bluetooth permissions are granted
• Shows a red Bluetooth icon when Bluetooth is disabled
• Shows a default Bluetooth icon when a profiled device is detected nearby
• Shows a blue "Bluetooth Connected" icon when a profiled device is connected via system Bluetooth
• Tapping the icon opens Android Bluetooth settings

Technical Context

• System Bluetooth connection state (BluetoothManager2.connectedDevices) is merged into PodDevice via DeviceMonitor, so the toolbar icon reacts as soon as the classic BR/EDR headset profile connects — it does not wait for the AAP handshake to complete
• The intent launch for Bluetooth settings is wrapped in a SecurityException catch for devices that gate settings access behind Bluetooth permissions
• connectedDevices is joined with onStart { emit(emptyList()) } so it doesn't block the initial combine emission while the StateFlow replays its first value