Web & Mobile Task Scheduler

I need a small-footprint scheduling engine that runs in both a web application and its companion mobile app. The system will let end-users set up and manage:

• meetings that push to their preferred calendar
• one-off or repeating reminders with configurable notifications
• fully recurring tasks (daily, weekly, custom)
• WhatsApp messages dispatched automatically through the WhatsApp Business API

Core expectations
• A single codebase or tightly aligned services so web and mobile stay in sync in real time.
• An intuitive UI for creating, editing, and canceling schedules.
• Reliable background execution—think server-side cron or queue workers on the web side and native schedulers / push on iOS and Android.
• Time-zone awareness, error logging, and basic analytics so I can monitor success or failure rates.
• Clean documentation plus a quick start guide for deploying to staging and production.

Acceptance will be based on:
1. Creating a task on one platform instantly visible on the other.
2. Correct firing of notifications and WhatsApp messages at the scheduled time, even after app restarts.
3. All code passing a short test suite and linting checks.

I’m comfortable with mainstream stacks such as Node.js, Python, Firebase, or comparable solutions—use whatever lets you meet the above criteria efficiently.