Cron explainer

Adds cron schedule explanations, including a new --explain CLI option that prints each crontab entry alongside a human-readable description of when it runs. The explainer supports common cron patterns, nicknames such as @daily, second-based schedules, named months/weekdays, ranges, lists, and nth weekday syntax. This branch also adds examples and test coverage for the new explanation behaviour.

What's Changed

• feature: explain crons closes #53 by @g105b in #73

Full Changelog: v1.2.0...v1.2.1