Adds a 'Cron' schedule type option to the scheduled task editor, allowing users to create and edit cron-based schedules through the UI. - Add cron expression input with inline validation (cron-parser) - Show next 4 upcoming run times as a preview - Provide clickable example chips (every 5min, hourly, Monday 9am, etc.) - Preserve cron expressions when editing existing cron tasks - Add cron.ts utility module for validation and next-run computation - Add i18n keys across all 8 locale files Closes #1586 Co-authored-by: Bohdan Triapitsyn <artmore@protonmail.com>