docs: add initial project plan and README

Added comprehensive implementation plan (PLAN.md) with 15 phases covering:
- Project setup with Next.js 16 and Tailwind CSS 4
- Web Audio API integration
- Waveform visualization
- Multi-track editing
- Audio effects and automation
- Recording capabilities
- Export/import functionality

🤖 Generated with [Claude Code](https://claude.com/claude-code)

Co-Authored-By: Claude <noreply@anthropic.com>

README.md

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+# Audio UI
+
+A sophisticated browser-only audio editor built with Next.js 16, React 19, and Tailwind CSS 4.
+
+## Features (Planned)
+
+- **100% Client-Side**: All audio processing happens in your browser
+- **Multi-Track Editing**: Professional multi-track audio editing
+- **Advanced Effects**: EQ, compression, reverb, delay, and more
+- **Automation**: Automate volume, pan, and effect parameters
+- **Recording**: Record audio directly from your microphone
+- **Analysis Tools**: Frequency analyzer, spectrogram, and loudness metering
+- **Export Formats**: WAV, MP3, OGG, FLAC
+- **Project Management**: Save and load complete projects
+- **Privacy-First**: No uploads, all data stays local in your browser
+
+## Tech Stack
+
+- **Next.js 16** with React 19
+- **TypeScript 5**
+- **Tailwind CSS 4** with OKLCH colors
+- **Web Audio API** for audio processing
+- **Canvas API** for waveform visualization
+- **IndexedDB** for project storage
+
+## Getting Started
+
+This project is currently in the planning phase. See [PLAN.md](./PLAN.md) for the complete implementation plan.
+
+### Development (Coming Soon)
+
+```bash
+# Install dependencies
+pnpm install
+
+# Run development server
+pnpm dev
+
+# Build for production
+pnpm build
+```
+
+## Inspiration
+
+Inspired by [AudioMass](https://github.com/pkalogiros/AudioMass) and professional DAWs like Ableton Live, Logic Pro, and FL Studio.
+
+## License
+
+TBD
+
+## Contributing
+
+This is a personal project, but suggestions and ideas are welcome!