Release v0.6.0

- Change default card storage from ~/Downloads to ~/.local/state/totalrecall/cards/
- Keep .apkg exports in ~/Downloads for user convenience
- Fix audio regeneration to use random voice and speed (0.9-1.0)
- Fix GNOME dock icon by updating StartupWMClass
- Fix navigation to properly find cards in new XDG state directory
- Ensure config defaults are properly filled when using GUI mode