fix(flatpak): allow reading launcher version pins

packaging/linux/flatpak/ai.storyteller.gridcraft.bundle.yml

@@ -17,6 +17,7 @@ runtime-version: '25.08'
 sdk: org.freedesktop.Sdk
 command: gridcraft
 finish-args:
+  - --filesystem=xdg-data/ArtCraft/versions:ro
   # Display: Wayland first; X11 only when no Wayland compositor is running.
   - --socket=wayland
   - --socket=fallback-x11