New TurnKey GitLab version (19.0)

Changes:

• Install GitLab CE 19.3.0 from its official Debian 13 repository with a pinned version, repository key fingerprint, and signed package metadata.
• Add a non-mutating update check and document GitLab's supervised required upgrade stops.
• Verify firstboot failures and keep the root password out of child process arguments.
• Add v19 application acceptance coverage and README evidence crosswalk.
• Upgrade the base distribution to Debian 13 Trixie.

Links

• Release meta-files (signature, manifest)