fix(deb): use apt-get instead of apt in setup scripts

[Martini991]

Problem

The Debian setup scripts run apt update and apt install. In non-interactive runs (Docker/Podman builds, CI, curl … | bash -) every call prints:

WARNING: apt does not have a stable CLI interface. Use with caution in scripts.

setup_lts.x prints it three times. apt is the interactive front end; apt(8) says:

The apt(8) commandline is designed as an end-user tool and it may change behavior between versions. […] So you should prefer using these commands [apt-get(8), apt-cache(8)] (potentially with some additional options enabled) in your scripts as they keep backward compatibility as much as possible.

apt-get is not deprecated. #1875 (for #1874) switched the scripts to apt on that premise; this PR goes back to apt-get for the commands the scripts run.

Change

• scripts/deb/script_generator/base_script.sh: apt update -y → apt-get update -y (twice) and apt install -y … → apt-get install -y …, with the matching comments and error message. Flags are unchanged.
• Regenerated setup_20/22/24/25/26.x, setup_lts.x and setup_current.x with generator.sh. Applied the same change by hand to setup_16/18/21/23.x, which the generator no longer produces.
• The hints shown to users (To install Node.js, run: apt install nodejs -y) are unchanged, since they are for interactive use.

The CI workflows still call apt; I can switch them too if you'd like.

Testing

• bash -n on all changed files.
• setup_lts.x in a clean debian:trixie-slim container, before and after:

	before (master)	after
"stable CLI interface" warnings	3	0
exit code	0	0
nodesource.sources, apt preferences, keyring	—	identical
apt-get install -y nodejs	v24.21.0 from NodeSource	v24.21.0 from NodeSource

Prepared with the help of Claude Code; I reviewed the change and ran the tests above.

[ns-control-tower]

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