Cross-Platform Productivity App Build

I’m ready to turn my concept for a productivity tool into a fully functioning mobile app that runs smoothly on both iOS and Android. At its core the app should let users create, organise and track tasks while syncing seamlessly with their existing calendars so deadlines and reminders appear in one place.

Here’s what I need delivered:
• A modern, intuitive UI/UX that makes task entry and calendar views effortless on phones and tablets.
• Core features: robust task management (lists, priorities, due dates, reminders) and real-time calendar integration (two-way sync with native device calendars and Google / Outlook where possible).
• Clean, well-documented code using a cross-platform framework (Flutter, React Native or similar) so future enhancements—such as time-tracking—can be added without a full rebuild.
• Basic analytics and crash reporting wired in from day one.
• Deployment to both App Store and Google Play, including help with initial store listings and test-flight / beta track setup.

Please outline your preferred tech stack, any similar productivity apps you’ve shipped, and how long you’d need for a first clickable prototype and final release. Let’s build something users will rely on every day.