enum FileDialog

Native "open"/"save" file picker.

Linux only, backed by zenity (GTK's own file chooser, invoked as a subprocess — the common approach for a GLFW/Vulkan app that has no GTK event loop of its own to host a real widget in). Blocks the calling thread until the user picks a file or cancels, same as any native modal dialog; call it from the main loop between frames, not from a paint closure. Returns nil on cancel, on a platform with no backend here, or if zenity isn't installed — callers should treat all three the same way ("no file chosen"), not surface them as distinct errors.