Update version to 2.99 in auto/config and fix APT sources

[rodw-au]

Add deb822 style sources to /apt/sources.list.d
remove /etc/apt/sources.list which is set to CD only
Update version to 2.99 in auto/config

[rodw-au]

Grr, sources.list was not deleted. I must have the hook in the wrong location. testing again

[rodw-au]

Don't ask me how many time sI built this before working this out!
Our choices in config/includes.installer/preseed.cfg was affecting how sources.list was generated.
This Debian forum thread helped me understand whats going on
https://forums.debian.net/viewtopic.php?t=167054
So now the CDROM line in sources.list is commented out leaving it as an empty file (except for comments). This lets apt to fall through to /etc/apt/sources.list.d/debian sources which we added manually and everything works with no errors.

But if a user who does not have internet installs this and uncomments the CDROM entry, apt will fail becasue of security.

Warning: The repository 'cdrom://[Debian GNU/Linux 13 _Trixie_ - Snapshot amd64 LIVE/INSTALL Binary 20260702-11:00] trixie Release' does not have a Release file.
Notice: Data from such a repository can't be authenticated and is therefore potentially dangerous to use.
Notice: See apt-secure(8) manpage for repository creation and user configuration details.
Error: Failed to fetch cdrom://[Debian GNU/Linux 13 _Trixie_ - Snapshot amd64 LIVE/INSTALL Binary 20260702-11:00]/dists/trixie/contrib/binary-amd64/Packages  Please use apt-cdrom to make this CD-ROM recognized by APT. apt-get update cannot be used to add new CD-ROMs

The reality is that there are no available packages in the generated ISO and it just confirms that its recommended internet connectivity is available when installing linuxCNC.

I have tested installation without internet connectivity previously and it works but I have not tested on this PR.

This issue closes Issue #38