v0.16.1 - Browser-Agent Validation And Readiness Explanations

Phase 16 adds standard-neutral browser-agent validation output for measuring whether Descuff materially improves how agents use a site.\n\nHighlights:\n- Browser-agent scenario evidence and before/after effort summaries.\n- Readiness explanations tied to concrete validation evidence.\n- Scenario boundary enforcement for allowed routes and origins.\n- Typed validation failures for safer automation and clearer reports.\n\nValidation:\n- CI passed.\n- Release checks passed.\n- Packed install smoke passed.\n- npm registry verification passed for 0.16.1.