docs: delete executed design specs and check every doc link

CONTRIBUTING.md

@@ -91,7 +91,7 @@ isolation.
 A change to `common/` or to an adapter reaches a project that already exists
 only when somebody runs `scaffold update` in it — see
 [ADR-0023](docs/decisions/0023-a-project-records-what-generated-it.md). A
-change to a reusable workflow in `you/.github` reaches every project the next
+change to a reusable workflow in *you/.github* reaches every project the next
 time it runs, once `v1` moves (ADR-0005). Knowing which of the two you are
 writing decides whether anything has to be done afterwards.
 

docs/PROVENANCE.md

@@ -44,9 +44,9 @@ Excluded, and why:
   file-by-file origin and licence — which is what a reader who finds the
   directory will actually look at. `docs/public/logo.png` comes from the same
   repository and the same `NOTICE` covers it.
-- **`docs/decisions/`, `docs/superpowers/specs/`** (this repository's own, at
-  the root — not `common/docs/decisions/`, which ships and is covered below).
-  These are this project's own record, not files copied from upstream.
+- **`docs/decisions/`** (this repository's own, at the root — not
+  `common/docs/decisions/`, which ships and is covered below). This is this
+  project's own record, not files copied from upstream.
 - **`lib/*.sh`, `scaffold`, `scripts/*.sh`, `tests/*.bats`, `mise.toml`,
   `mise.lock`, `lefthook.yml`, `.github/workflows/*.yml`** (this repository's
   own CI and hooks, not `common/.github/workflows/` or `common/lefthook.yml`,