feat: design system v2 with liquid glass aesthetic

Overhaul design constants for OLED-first dark mode:
- Colors: brand palette, phase colors, glass/shadow tokens, gradients
- Typography: Inter font scale matching iOS type system
- Spacing: 4px base unit with layout constants
- Border radius: liquid glass card radii
- Animations: spring/timing presets for UI transitions

Add v2 product docs (PRD, PDD, BDSD) and update CLAUDE.md.
Install expo-video, expo-sharing, @expo-google-fonts/inter.

Co-Authored-By: Claude Opus 4.6 <noreply@anthropic.com>

README.md

@@ -1,50 +1,75 @@
-# Welcome to your Expo app 👋
+# TabataFit
 
-This is an [Expo](https://expo.dev) project created with [`create-expo-app`](https://www.npmjs.com/package/create-expo-app).
+> **Apple Fitness+ for Tabata** — The Premium HIIT Experience
 
-## Get started
+![Expo](https://img.shields.io/badge/Expo-52-black)
+![TypeScript](https://img.shields.io/badge/TypeScript-5.0-blue)
+![License](https://img.shields.io/badge/License-Proprietary-red)
 
-1. Install dependencies
+## Vision
 
-   ```bash
-   npm install
-   ```
+TabataFit est l'Apple Fitness+ du Tabata. Une expérience premium, video-first, guidée par des coachs, qui transforme 4 minutes d'exercice en une expérience de fitness immersive.
 
-2. Start the app
+## Features
 
-   ```bash
-   npx expo start
-   ```
+- 🎬 **Video-led workouts** — HD video demonstrations by professional trainers
+- ⏱️ **Smart timer** — Tabata timer with work/rest phases
+- 🔥 **Burn Bar** — Compare your calories with the community
+- 📊 **Activity tracking** — Streaks, stats, and trends
+- 🎵 **Music sync** — Curated playlists for each workout
+- ⌚ **Apple Watch** — Heart rate and activity rings
 
-In the output, you'll find options to open the app in a
+## Tech Stack
 
-- [development build](https://docs.expo.dev/develop/development-builds/introduction/)
-- [Android emulator](https://docs.expo.dev/workflow/android-studio-emulator/)
-- [iOS simulator](https://docs.expo.dev/workflow/ios-simulator/)
-- [Expo Go](https://expo.dev/go), a limited sandbox for trying out app development with Expo
+- **Framework**: Expo SDK 52
+- **Navigation**: Expo Router v3
+- **State**: Zustand
+- **Video**: expo-av (HLS streaming)
+- **Payments**: RevenueCat
+- **Analytics**: PostHog
 
-You can start developing by editing the files inside the **app** directory. This project uses [file-based routing](https://docs.expo.dev/router/introduction).
-
-## Get a fresh project
-
-When you're ready, run:
+## Getting Started
 
 ```bash
-npm run reset-project
+# Install dependencies
+npm install
+
+# Start development server
+npx expo start
+
+# Run on device (scan QR with Expo Go)
 ```
 
-This command will move the starter code to the **app-example** directory and create a blank **app** directory where you can start developing.
+## Documentation
 
-## Learn more
+| Document | Description |
+|----------|-------------|
+| [PRD v2.0](./TabataFit_PRD_v2.0.md) | Product Requirements |
+| [PDD v2.0](./TabataFit_PDD_v2.0.md) | Product Design |
+| [BDSD v2.0](./TabataFit_BDSD_v2.0.md) | Brand Design |
 
-To learn more about developing your project with Expo, look at the following resources:
+## Project Structure
 
-- [Expo documentation](https://docs.expo.dev/): Learn fundamentals, or go into advanced topics with our [guides](https://docs.expo.dev/guides).
-- [Learn Expo tutorial](https://docs.expo.dev/tutorial/introduction/): Follow a step-by-step tutorial where you'll create a project that runs on Android, iOS, and the web.
+```
+src/
+  features/
+    home/        # Home tab
+    workouts/    # Workouts browser
+    player/      # Video player + timer
+    activity/    # Stats & history
+    browse/      # Filters & trainers
+    profile/     # User settings
+  shared/
+    components/  # Reusable UI
+    hooks/       # Custom hooks
+    constants/   # Design tokens
+app/             # Expo Router routes
+```
 
-## Join the community
+## License
 
-Join our community of developers creating universal apps.
+Proprietary — All rights reserved.
 
-- [Expo on GitHub](https://github.com/expo/expo): View our open source platform and contribute.
-- [Discord community](https://chat.expo.dev): Chat with Expo users and ask questions.
+---
+
+Built with ❤️ for HIIT lovers