Move LGM to Codeberg

[unfa]

As discussed and voted on during LGM2026.

[aoloe]

I've now crated an organization on Codeberg:

https://codeberg.org/libregraphicsmeeting

[aoloe]

As discussed in Nuremberg, the idea seems to be move all our repositories from Github to Codeberg.

I would suggest to:

• duplicate all the repositories on Codeberg
• mark the Github repositories as deprecated
• at some time in the future delete the repositories on Github (I would leave one single repository as a placeholder and with the only content that the LGM is now on Codeberg)