Implement Feature Flags with LaunchDarkly Pattern

Implement a feature flag system following the LaunchDarkly pattern. Include:

1. **Flag evaluation engine:**
   - Support flag types: boolean, string, number, JSON
   - User targeting by attributes (id, email, plan, country)
   - Percentage rollouts with consistent hashing
   - Rule-based targeting with AND/OR conditions
   - Default values when flag is not found

2. **React integration:**
   - FeatureFlagProvider context wrapper
   - useFeatureFlag(flagKey, defaultValue) hook
   - FeatureGate component for conditional rendering
   - withFeatureFlag HOC for class components

3. **Server-side evaluation:**
   - Middleware for API routes
   - Flag evaluation in server components
   - Edge-compatible evaluation

4. **Management:**
   - In-memory store with API-driven updates
   - Flag change event streaming
   - Local override for development
   - Analytics tracking of flag evaluations

Use TypeScript throughout with proper generics.