Add comprehensive user profile and onboarding system with secure health data management

.env.example

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+# Environment Variables Example
+# Copy this file to .env for local development
+
+# App Configuration
+APP_NAME=Nutrition App
+APP_VERSION=1.0.0
+
+# Feature Flags (if needed in future)
+ENABLE_ANALYTICS=false
+ENABLE_CLOUD_SYNC=false
+
+# Note: This app stores all data locally and doesn't require API keys
+# Add any future API keys or configuration here

.eslintrc.js

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+module.exports = {
+  root: true,
+  extends: [
+    '@react-native',
+  ],
+  rules: {
+    'prettier/prettier': 'off',
+    'react-native/no-inline-styles': 'off',
+    'no-console': ['warn', { allow: ['warn', 'error'] }],
+  },
+};

.gitignore

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+# OSX
+#
+.DS_Store
+
+# Node
+node_modules/
+npm-debug.log
+yarn-error.log
+package-lock.json
+yarn.lock
+
+# React Native
+#
+.expo/
+.expo-shared/
+ios/Pods/
+ios/build/
+android/app/build/
+android/.gradle/
+android/build/
+android/local.properties
+
+# Build artifacts
+*.jks
+*.p8
+*.p12
+*.key
+*.mobileprovision
+*.orig.*
+web-build/
+dist/
+
+# Debug
+npm-debug.*
+yarn-debug.*
+yarn-error.*
+
+# Bundle artifacts
+*.jsbundle
+
+# CocoaPods
+ios/Pods/
+
+# Temporary files
+*.tmp
+*.temp
+.tmp/
+.temp/
+
+# IDE
+.vscode/
+.idea/
+*.swp
+*.swo
+*~
+
+# Tests
+coverage/
+.nyc_output/
+
+# Environment
+.env
+.env.local
+.env.*.local

ARCHITECTURE.md

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+# Nutrition App Architecture
+
+## Overview
+
+This is a React Native mobile application built with Expo that provides a comprehensive user onboarding system for collecting health and nutrition data.
+
+## System Architecture
+
+### Data Flow
+
+1. **Privacy Policy** → User must accept before proceeding
+2. **Onboarding Flow** → 6-step data collection process
+3. **Profile Storage** → Encrypted local storage
+4. **Home Dashboard** → Display user data and insights
+5. **Profile Management** → Edit and update profile
+
+### Component Hierarchy
+
+```
+App.tsx (Root)
+├── PrivacyPolicyScreen
+└── NavigationContainer
+    ├── OnboardingContainer
+    │   ├── ProgressIndicator
+    │   ├── Step1BasicInfo
+    │   │   └── SingleSelectList
+    │   ├── Step2ActivityLevel
+    │   │   └── SingleSelectList
+    │   ├── Step3NutritionGoals
+    │   │   └── MultiSelectList
+    │   ├── Step4MedicalConditions
+    │   │   └── MultiSelectList
+    │   ├── Step5FoodAllergies
+    │   │   └── MultiSelectList
+    │   └── Step6DietaryPreferences
+    │       └── MultiSelectList
+    ├── HomeScreen
+    └── ProfileEditScreen
+```
+
+## Data Model
+
+### UserProfile
+
+The core data structure that stores all user information:
+
+```typescript
+interface UserProfile {
+  // Demographics
+  age: number;
+  weight: number; // kg
+  height: number; // cm
+  gender: Gender;
+
+  // Activity & Goals
+  activityLevel: ActivityLevel;
+  nutritionGoals: NutritionGoal[];
+
+  // Health Information
+  medicalConditions: MedicalCondition[];
+  foodAllergies: FoodAllergy[];
+  dietaryPreferences: DietaryPreference[];
+
+  // Metadata
+  createdAt: string;
+  updatedAt: string;
+}
+```
+
+## Security Implementation
+
+### Encryption
+
+- **Storage**: Expo SecureStore (iOS Keychain / Android Keystore)
+- **Encryption Method**: Hardware-backed AES-256 encryption (OS-level)
+  - iOS: Uses Keychain Services with kSecAttrAccessibleWhenUnlockedThisDeviceOnly
+  - Android: Uses EncryptedSharedPreferences with Android Keystore
+- **Integrity Verification**: SHA-256 hashing to detect data tampering
+
+### Data Protection
+
+1. **Local Only**: All data stored on device
+2. **No Transmission**: Data never sent to servers
+3. **User Control**: Users can delete data anytime
+4. **Encrypted**: Health data encrypted at rest
+
+## Validation System
+
+### Three-Level Validation
+
+1. **Field Validation**
+   - Age: 13-120 years
+   - Weight: 20-300 kg
+   - Height: 100-250 cm
+   - Required fields
+
+2. **Logical Consistency**
+   - Conflicting dietary preferences (vegan + keto)
+   - Medical condition alignment
+   - Allergy-diet correlation
+
+3. **Health Recommendations**
+   - BMI-based goal suggestions
+   - Medical condition warnings
+   - Safety recommendations
+
+## Screen Flow
+
+### First Launch
+```
+Privacy Policy → Onboarding (Step 1-6) → Home Dashboard
+```
+
+### Returning User
+```
+Home Dashboard ↔ Profile Edit ↔ Onboarding (Edit Mode)
+```
+
+### Profile Management
+```
+Home → View Profile → Edit Profile → Re-run Onboarding
+```
+
+## Technology Stack
+
+### Core Technologies
+- **React Native**: Cross-platform mobile framework
+- **Expo**: Development platform and SDK
+- **TypeScript**: Type-safe development
+- **React Navigation**: Navigation management
+
+### Key Libraries
+- `expo-secure-store`: Encrypted storage
+- `expo-crypto`: Cryptographic operations
+- `@react-navigation/native`: Navigation
+- `@react-navigation/stack`: Stack navigation
+
+### Development Tools
+- **Jest**: Testing framework
+- **ESLint**: Code linting
+- **TypeScript**: Static typing
+- **Metro**: JavaScript bundler
+
+## Onboarding Steps
+
+### Step 1: Basic Demographics
+- Age input (number)
+- Weight input (decimal)
+- Height input (number)
+- Gender selection (radio)
+
+### Step 2: Activity Level
+- Single selection from 4 options
+- Descriptive text for each level
+
+### Step 3: Nutrition Goals
+- Multiple selection allowed
+- 5 goal options
+
+### Step 4: Medical Conditions
+- Multiple selection
+- 8 condition options
+- Informational disclaimer
+
+### Step 5: Food Allergies
+- Multiple selection
+- 11 allergy options
+- Safety warning
+
+### Step 6: Dietary Preferences
+- Multiple selection
+- 10 preference options
+- Conflict validation
+- Completion action
+
+## Extensibility
+
+### Adding New Options
+
+1. Update type definitions in `src/types/UserProfile.ts`
+2. Add options to `src/constants/options.ts`
+3. Update validation in `src/utils/validation.ts`
+
+### Adding New Steps
+
+1. Create new step component in `src/screens/onboarding/`
+2. Add to `OnboardingContainer.tsx`
+3. Update `ONBOARDING_STEPS` constant
+4. Add validation logic
+
+### Customizing Validation
+
+Validation rules are centralized in `src/utils/validation.ts`:
+- `validateBasicDemographics()`: Field-level validation
+- `validateDietaryPreferences()`: Conflict detection
+- `validateConsistency()`: Cross-field validation
+
+## Best Practices
+
+### Security
+- Never log sensitive health data
+- Always use SecureStore for health info
+- Validate all user inputs
+- Provide clear privacy disclosures
+
+### UX
+- Show progress indicator
+- Allow navigation backward
+- Provide helpful descriptions
+- Display validation errors clearly
+
+### Development
+- Use TypeScript for type safety
+- Write tests for validation logic
+- Keep components focused and reusable
+- Follow React Native best practices
+
+## Future Enhancements
+
+### Potential Features
+- Data export functionality
+- Cloud backup (optional, with consent)
+- Integration with health apps
+- Meal plan generation
+- Progress tracking
+- Calorie calculator
+- Nutrition insights
+
+### Technical Improvements
+- Stronger encryption algorithm
+- Biometric authentication
+- Offline sync capabilities
+- Analytics (privacy-preserving)
+- A/B testing framework
+- Performance optimization