v0.1.0

fix: discover the host flatpak installation when running sandboxed

Inside a flatpak, XDG_DATA_HOME points at our own private data, so the
user-installation scan (and override writes) missed every user-installed
app, including FlatKontrol itself. Use HOST_XDG_DATA_HOME and the host
/etc path when running in a sandbox, matching Flatseal.