New TurnKey Jenkins version (19.0)

Changes:

• Install Jenkins 2.568.2 LTS from its official repository with a pinned version, bound 2026 signing key, and signed package metadata.
• Run Jenkins on Debian Trixie's OpenJDK 21 and retain Git, Subversion, Pipeline, mail, and build support.
• Keep firstboot credentials out of process arguments and propagate password update failures.
• Add a non-mutating LTS update check, v19 acceptance coverage, and README evidence crosswalk.
• Upgrade the base distribution to Debian 13 Trixie.

Links

• Release meta-files (signature, manifest)