feat: Rollout system

A/B testing should be made simple. feature flag system in framework to slowly rollout breaking/risky stuff, but operators like central will also need control of this too to do phased rollouts.
Needs research before starting.

No files, tests, or entry points are named. Start by researching the requirements for framework feature flags, gradual rollouts, and Central operator control, including how phased rollouts should be managed. Done means producing an agreed design and scope before implementation begins.

Written by the indexing model from the issue text.