fix(flatpak): allow reading launcher version pins

packaging/linux/flatpak/ai.storyteller.effectcraft.yml

@@ -20,6 +20,7 @@ sdk-extensions:
   - org.freedesktop.Sdk.Extension.rust-stable
 command: effectcraft
 finish-args:
+  - --filesystem=xdg-data/ArtCraft/versions:ro
   # Display: Wayland first; X11 only when no Wayland compositor is running.
   - --socket=wayland
   - --socket=fallback-x11