Add "For app-side implementation" paragraph so the completion plan can
be used in the app repo: focus §2/§3, plugin v2.1.0+, link/build check,
Edit flow with updateDualScheduleConfig, and key app file paths.
- Checklist for completing dual-schedule (New Activity) on plugin and app
- Context: two notification types (Daily Reminder vs New Activity), isolation
- iOS: cron parsing, relationship, cancelDualSchedule, updateDualScheduleConfig
- Android: cancelDualSchedule; updateDualScheduleConfig for Edit time
- Consuming app: link/build verification, Edit flow use updateDualScheduleConfig
- Replace semantics and refs to plugin and app code