External control for LEDs via HID Reports

Added a new "External" LED source to FreeJoy, enabling host software to control up to 24 LEDs directly via HID Output Reports. This feature is useful for applications where LED states need to be synchronized with game events or external logic rather than being tied to physical buttons or axes.

This feature is supported by FreeJoy Configurator (FreeJoy-Team/FreeJoyConfiguratorQt#45) and is fully documented in the Wiki (FreeJoy-Team/FreeJoyWiki#89).