Phase 17.3: PredictiveEngine wiki page (138th) + sidebar update - Phase-17-Predictive-Engine.md: full spec (PredictionStrategy enum, Prediction/PredictionError/PredictorConfig frozen dataclasses, PredictiveEngine Protocol @runtime_checkable, AdaptivePredictiveEngine EMA+linear trend+ensemble weighting+online gradient descent+calibrate(), NullPredictiveEngine, EMA formula diagram, ensemble weight evolution, 5 Prometheus metrics+PromQL+Grafana alert, mypy table, 12 test targets+ 2 skeletons, 14-step impl order, Phase 17 sub-phase tracker) - _Sidebar.md: add PredictiveEngine link under Phase 17 section Issue: #440 | Show & Tell: #441 | Q&A: #442