flatpak: Unable to change theme at runtime with `--theme`

[tello2004]

This only happens in the Flatpak version of Lagrange.

As I was trying to get Lagrange theme to match my system color scheme, I stumbled upon one particular issue: I was not able to change the theme of a running instance with the --theme flag. It's not just --theme, obviously, listing all tabs with L does not work too and so the other runtime flags.

Grabacion.de.pantalla.desde.2026-05-02.13-05-09.webm

[skyjake]

This is likely due to the sandboxing Flatpak forces on the app. It would need a native inter-process communication support (like D-Bus) to work properly.