Add themed icon.



## Device information
* Kotatsu version: 9.6.10
* Android version: 15
* Device: oneplus 5t

## Steps to reproduce
1. No specific instructions.

## Issue/Request
Suggesting to add monochrome layer to the app icon in order for it to be themable on modern Android versions.

For reference: https://developer.android.com/develop/ui/views/launch/icon_design_adaptive

## Other details
None
