docs(roadmaps): add AI diagnostic assistant, A/B testing, and churn prediction roadmaps
- AI Diagnostic Assistant: LLM-powered root cause analysis, error clustering, natural language queries
- Intelligent A/B Testing: Thompson sampling, Bayesian early stopping, AI hypothesis generation
- Predictive Churn & Health: XGBoost models, health scoring, automated retention campaigns
All roadmaps include:
- Implementation tracking tables with status/commit columns
- Quick reference sections with file structures
- Phase-by-phase task breakdowns with [X.Y.Z] codes
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