Extracts pure, click-free cargo-cache status/purge and host disk/runner/
backup-template logic into operations/, mirroring the W1 pattern. Routes
commands/retention.py::_purge_cargo_cache through operations.cache while
preserving identical CLI output. commands/monitor.py is left untouched
(its refactor is optional per the plan; the Windows/Linux polymorphic
_service_status and the disk not-found detection don't map cleanly onto
the new pure functions without risking behavioural drift).
