DR-086a — The cocoindex qa_sidecar route is fully retired (walk-side AND app-side write half)

The qa_sidecar concept is retired in FULL. Walk-side removed by {127.37}: the .kh-workspace-map.json manifest, folder→workspace resolution (workspace_resolver.py), workspace_id tagging, and the qa_sidecar route/branch are gone. The app-side WRITE half landed too ({127.38}, closed S494): no app code derives or mints a __qa__/ sidecar path (app/api/q-a-pairs/[id]/route.ts:17-21, lib/q-a-pairs/promote-corpus.ts). Rationale: DR-038/056/061 (workspace is the wrong scope; per-client single-tenant DB needs no in-DB scoping predicate). Fully discharged; retired at the S499 owner review.

Substance now lives in: canonical:app/api/q-a-pairs/[id]/route.ts:17-21 + lib/q-a-pairs/promote-corpus.ts