cd2ab1c4b6
KeyData.key was a raw u32 carrying SDL_Keycode values, so app code had to reinterpret it as SDL_Keycode (xx e.key) — a leaky, unchecked cross-platform cast only valid because the backend happened to be SDL. Add a neutral Keycode enum; translate_sdl_event maps SDL_Keycode to it via keycode_from_sdl. App code compares e.key == .escape with no platform type and no cast; a new backend maps its own native codes in one place.