Hard and Soft Links: Roll a Release Forward

This box runs releases side by side under /srv/app/releases, and /srv/app/current is a symbolic link that says which one is live. Release 2.5.0 is ready. Three link fixes finish the rollout:

1. Point /srv/app/current at release 2.5.0. It must stay a symbolic link.

2. The command /usr/local/bin/appctl is a dangling symlink from an old install. Make it a symbolic link that goes through /srv/app/current, so that running appctl reports 2.5.0 now and follows current on every future upgrade without being touched again.

3. /srv/app/shared/app.conf is a stale copy of /etc/app/app.conf. Replace it with a hard link to /etc/app/app.conf (which holds the live settings), so both names are the same file and can never drift apart.

Grading checks the links themselves (what each points to and which inode each name uses), not just whether a file happens to have the right content.