Feature Flag System

This implements a complete feature flag system for controlling rollouts, A/B tests, and kill switches. You get flag evaluation with rules based on user attributes, percentages, and time windows, plus variant support for experiments. The references include a TypeScript service, React hooks, analytics integration, and even an admin UI. Honestly, this is the kind of thing you'd normally reach for LaunchDarkly or Split for, but if you need flags without the SaaS dependency or want full control over the data, this gives you a solid foundation. Just don't forget the cleanup part, abandoned flags pile up fast.