Move session scans, timeout handling, refresh scheduling, and snapshot state
into an autonomous QML controller. Keep the existing refresh policy and
normalize bounded responses in a pure module. Preserve the applet-facing
presentation while removing Sessions from the shared usage dispatcher.

Exercise the production controller with real timers and synthetic CLI requests,
including command changes, retained snapshots, cooldowns, and timeout recovery.

Documentation impact: update the development ownership and test guide; regenerate
catalog source references with unchanged translations. User behavior, config,
README, usage guide, changelog, and parity TODO remain unchanged.