Extends report_build.py with build_by_kind() (per-scenario-kind pass/fail
rollup) and a ported build_stress()/stress_headline()/stress_plots() (scaling
curves per stress axis), wires both into the headline KPIs, regression
tracking, and report_data.json. E2E_Report.typ renders the four new
per-kind tables plus a Stress Tests section (per-axis case tables + scaling
plots, gracefully degrading to placeholders when a kind/stress data is
absent). run_e2e.sh now passes --stress-results so the report actually
receives real stress data instead of silently omitting it.
Co-Authored-By: Claude Opus 4.6 <noreply@anthropic.com>