Complete HarmonyOS app development guide with ArkTS, Stage model, and ArkUI. Use when:
- Creating new HarmonyOS projects ("Set up a new HarmonyOS project")
- Developing UI with ArkUI components and state management
- Integrating system capabilities (window, file, background tasks)
- Adding media services (audio, video, camera)
- Deploying to multiple devices with responsive layouts
- Building cross-device collaboration features
Use with harmonyos-design-guidelines for complete design+development workflow.