UPDATE_STATE_FILE: Path = DEFAULT_STATE_DIR 'update_state.json'Persistent flags for the update-notification UX.
Tracks which version the user has been notified about (notified_version,
notified_at) and the most recent version they've seen the splash for
(seen_version, seen_at). Read by should_notify_update and friends
to suppress repeat notifications across invocations. Auto-update opt-outs
live in config.toml, not here.