Respect user-selected data directory location

MakeMKV flatpak fails to respect user preference for data directory location.

Steps to reproduce:
1. Open MakeMKV preferences
2. Set data directory to alternate path and close application
3. Re-open and find all preferences reset since app seeks data dir in /home/${USER}/.MakeMKV

Also, rather than defaulting to /home/${USER}/.MakeMKV, shouldn't the default location for the data directory be /home/${USER}/.var/app/com.makemkv.MakeMKV/.MakeMKV thereby more closely adhering to flatpak confinement conventions?

No source files or tests are named. Start by reproducing the preference reset using the listed steps and inspect how the Flatpak app resolves its data directory; done means an alternate location persists after reopening and the default follows the expected confined location.

Written by the indexing model from the issue text.