Add On-Screen Controls

Part of requirement FR3 ↗

User Story: As a user, I want the terminal's remote control interface to include directional buttons and an OK button, so that I can navigate menus and select options directly, without a mobile device connection.

Acceptance Criteria:

• The terminal indicates that it is ready to execute commands on button presses when a configuration is loaded.
• The terminal's physical buttons execute corresponding commands when pressed.