Move MVP workplan index out of workplans/ for ADR-001 compliance.

workplans/*.md must be YAML-frontmatter workplan files. The human index
lives at docs/mvp-workplans-index.md instead.

README.md

@@ -66,7 +66,7 @@ pnpm build      # production bundle
 ## Workplans (Ralph)
 
 Workplans drive incremental implementation through the ralph loop. The harness
-lives in `~/ralph-workplan/`; see `workplans/README.md` for the active list
+lives in `~/ralph-workplan/`; see `docs/mvp-workplans-index.md` for the active list
 and ordering.
 
 ```bash