Implement feature flags system with gradual rollout capability

[Smartdevs17]

Description

New features are deployed to all users at once with no ability to gradually roll out or A/B test. Implement a feature flag system with targeting rules.

Acceptance Criteria

• Feature flag management API with CRUD operations
• Targeting rules (percentage, user segment, environment)
• Client-side flag evaluation with caching
• Gradual rollout with auto-increase schedules
• A/B test assignment and tracking
• Flag usage analytics and stale flag detection

Technical Scope

• backend/src/services/featureFlags.ts
• backend/src/routes/flags.js
• frontend/lib/hooks/
• Edge: flag evaluation performance, flag configuration conflicts, flag cleanup