Follow-up to the contributor change that moves shell customization out of
per-user home directories:
- Migrate the resolute, trixie, and questing (+ slim) dev images to the
shared install-bashrc.sh; the shared create-users.sh now hands users a
minimal skeleton, so images still writing to /etc/skel/.bashrc would
otherwise lose their aliases and prompt.
- Restore export PATH="$PATH:$HOME/.local/bin" (needed for claude/gh) in
the full dev images by writing it to /etc/bash.bashrc; kept out of the
slim and production images, which never had it.
- Guard the /etc/skel/.config copy in create-users.sh so production images
without it don't emit a spurious error, and use rm -f /root/.bashrc.
- Fix the install-bashrc.sh header reference and silence an intentional
SC2016 on the runtime-expanded PS1.
