refactor(core,experts): classify except Exception + structured ReviewResult (U3)
ReviewResult dataclass (passed/degraded/feedback) replaces tuple+[DEGRADED] prefix in _review_phase_output; 3 review_result WS payloads now carry degraded field (AE3).
except Exception narrowed to specific types across 10 files (core/react, rewoo, base, orchestrator, dispatcher, plan_exec_engine + experts/orchestrator, _phase_executor, _review_gate + orchestrator/pipeline_engine). Baseline 140 -> 66 occurrences (>=50% reduction).
Fix RuntimeError regression: review-gate + compression paths now catch RuntimeError (LLM/provider internal errors) to preserve degradation semantics. Test side_effect switched to functional form to avoid StopIteration on list exhaustion.
ruff clean; 135 key + 469 experts + 163 core tests pass.
be5c4e09f8