Fix X11 for Meld/compareWith

[spoltier]

@spoltier, see some minor feedback.

I actually tried this for SmaRP, things seem to work fine with the exception of using Meld within the container

(meld:1038): dbind-WARNING **: 13:59:04.184: Couldn't connect to accessibility bus: Failed to connect to socket /run/user/1001/at-spi/bus: No such file or directory
Trace/breakpoint trap (core dumped)

It looks like the existing instructions about DISPLAY and X11 stuff don't work. Happy to open a separate issue for this.

Agree. I am able to reproduce this error now, but I was able to use Meld + compareWith when testing previously.
I tried older container images but these also show the same behavior. I suspect a patch on the host system may have changed the behavior - X11 is considered insecure and may be more restricted by default on up-to-date systems.
On 24.04 (VM), I also get a different error:

Originally posted by @spoltier in #48 (comment)