Introduce a tiny generic qa-runtime seam for shared live-lane helpers and
repoint qa-matrix to it. This keeps the qa-lab host split while removing
the host-owned runtime name from runner code.
Drop the old qa-lab-runtime shim/export now that nothing consumes it and
keep the plugin-sdk surface aligned with the new seam.
Drop the generated qa-runner catalog and the missing/install placeholder
path for repo-private QA runners. The host should discover bundled QA
commands from manifest plus runtime surface only.
Also trim stale qa-matrix install docs and package metadata so the
source-only QA policy stays consistent.
