Cross-Platform Productivity App Development

I need a skilled full-stack mobile developer to create a productivity tool available on both iOS and Android.

Essential features to include:
- Task management
- Calendar integration
- File sharing

Ideal skills and experience:
- Expertise in mobile app development for iOS and Android
- Experience with task management and productivity tools
- Strong UI/UX design skills
- Android Developer (Kotlin + Firebase expert)
- Backend Developer (Firebase / Node.js Cloud Functions)
- Web Developer (React.js or HTML Admin Panel)
- UI/UX Designer (optional but useful)
- QA Tester (optional for later)