Move the maintained gallery into a readable .ebox fixture and make ebox-playground own generic parsing, file mode, and public rendering. Keep the startup mode trigger deferred through the user's use-package configuration.
Verified with ebox-playground make check (6/6), etaf-playground make check (6/6), exact use-package startup harness, and fullscreen GUI capture at /tmp/ebox-playground-dsl-gallery.png.
