Same bug as the previous filebrowser/fmd fix: vaultwarden, immich,
audiobookshelf, homebox, rustdesk, emby, meshcentral, traccar, lyrion,
actualbudget, mealie, joplin, jellyfin, unifi, and ntfy all showed "Manage
that install (update / full reinstall / cancel)" when re-run against an
existing install, but choosing "1) Manage" fell straight through into the
same unconditional fresh-install flow every time regardless of choice —
no way to actually cancel or update in place. Wired all 15 up to
prompt_reinstall_mode, matching the reference pattern in
services/mattermost.sh: update pulls + restarts the existing container
without touching config, cancel leaves the install untouched, fresh falls
through to the existing full-install flow unchanged.
Also add `setup.sh --status`: a plain-text listing of every service with
its install state, using the exact same is_installed() calls the whiptail
checklist's [installed] marker uses. Exists so "is X actually installed"
can be answered by reading terminal output directly, without depending on
a whiptail checklist screen where a narrow/resized terminal can truncate
the "[installed]" suffix off-screen with no visible sign that happened.