Lets a server be cleanly removed from agent management: uninstall.sh
stops/disables the systemd timer and deletes the unit files, the
installed script, and the credentials env file, without touching the
server's entry or task history in the app. install.sh now prints the
uninstall command on success, and the Servers page has an "Uninstall"
button that reveals the same command (safe to show anytime since it
carries no secret).
Lets users log tasks the Linux agent can't discover on its own (e.g.
Docker-based backup jobs) directly in the UI. Tasks now carry an
origin ('agent' | 'manual') so the agent's report-sync logic only
ever creates/updates/stale-marks agent-sourced rows, leaving manual
entries untouched; the API rejects edits/deletes of agent-sourced
tasks to keep that boundary enforced server-side too.
bobban