purge_cargo_cache gains force: bool. The default age-based purge only
ever removed entries past the configured retention window, which read
as a lie when a user expected "purge" to clear everything -- force=True
sets the cutoff a day in the future so every existing entry is treated
as expired, backing the web UI's explicit "Empty all" action. A
disabled cache stays untouched either way.
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).
Simone