feat(variation): expose confidence dispersion metrics

[d-sorgcodexagent]

Summary

• expose RMS radius, largest principal sigma, and Gaussian position-content ellipsoid-volume dispersion metrics in PyQt6 and React
• add confidence-aware units, adequacy/unavailable reporting, selected-point dense-ranked low-variability intervals, and metric threshold/duration/sample controls
• add strict Python/TypeScript plot-definition v2 contracts, authentic v1 migration, complete applicability validation, and reproducible exports
• retain the localized-locus authoring and trusted production-Worker browser stack from parent feat(variation): author localized torque loci #4414

Verification

• 1,163 Python/PyQt tests on the approved dispersion head; 338 combined integration tests
• 804 React tests on the approved dispersion head; 841 combined integration tests
• exact Python 3.12 / MyPy 1.13 23-source gate
• TypeScript, ESLint, Vite build, Ruff/format, docs governance, secrets, diff/conflict
• 5 real Chromium production-Worker workflows
• all 61 cumulative changed code/test files <=400 LOC
• independent exact-head and merged-head GO reviews

Stack

Draft child of #4414. Full rendered confidence-ellipsoid meshes, broader cross-browser/AT and PyQt visual baselines, React localized execution/export, Rust parity, complete raw state/event/torque persistence, and remaining #4142 work stay open.