Avoid leaking snap environment values and in particular the `$SNAP*`
values to the children that we run from the terminal.

Do this programmatically instead of the launcher, since ghostty needs
know the environment it runs in, while it must not leak the info to the
children.

We've also another leak on snap, that creates a more visible problem
(wrong matching of children applications) that is the apparmor security
profile.

I've handled it at
https://github.com/3v1n0/ghostty/commit/cc3b46f6001aa9539508a1e82ebb85a588c6c4f2
but that requires some love in order to fully decouple the snap option
to the build, to avoid including it in non-snap builds, so an help would
be appreciated there.

> This PR was contains code (in `filterSnapPaths`) that was improved by
DeepSeek.

This is my third (!) attempt at implementing localization support. By
leveraging GTK builder to do most of the `gettext` calls, I can avoid
the whole mess about missing symbols on non-glibc platforms.

Added some documentation too for contributors and translators, just for
good measure.

Supersedes #5214, resolves the GTK half of #2357

This is my third (!) attempt at implementing localization support.
By leveraging GTK builder to do most of the `gettext` calls, I
can avoid the whole mess about missing symbols on non-glibc platforms.

Added some documentation too for contributors and translators,
just for good measure.