Full VM installs and Test Sandbox full mode now record a short
post-install runtime observation (60s settle + 120s sampling) with an
explicit measured/unavailable/failed/interrupted status that never
rewrites install success. Adds the standalone scripts/measure-runtime.py
sampler, the measure-installed-runtime.py harness wrapper, E2E report
rendering, results-API summaries, CI coverage and METRICS.md accounting
boundaries.