posthog-core-workflow-b

Implement PostHog feature flags, A/B experiments, and cohort management. Use when rolling out features with flags, running A/B tests, creating cohorts, or evaluating multivariate experiments with PostHog. Trigger: "posthog feature flag", "posthog experiment", "posthog A/B test", "posthog cohort", "feature rollout posthog", "posthog multivariate".