[Feature] Support Keyboard Input Mapping to 8 In-Game Buttons

### Is your feature request related to a problem?

I'm building a physical 8-key attachment for tablets that works by simulating keyboard presses (via USB). To make it usable with AstroDX, please add support for mapping arbitrary keyboard keys to the 8 in-game touch buttons.

### Describe the feature

A simple config file or in-app settings would suffice. Suggested default layout: A S D F for left 4, J K L ; for right 4, but user-customizable is ideal.

### Reason for adding

I'm building a physical 8-key attachment for tablets that works by simulating keyboard presses (via USB). To make it usable with AstroDX, please add support for mapping arbitrary keyboard keys to the 8 in-game touch buttons.

### Example(s)

_No response_

### Additional context

_No response_

Look for the input handling code, likely in a class managing touch or button presses. The feature requires adding keyboard event listeners and mapping them to the existing 8 button actions. Check if there's already a settings or configuration system to extend. Test by building and running the game, then pressing the suggested default keys to see if they trigger the correct button actions.

Written by the indexing model from the issue text.