♻️ Run doc-test generation as an explicit CI step

Drop the `pretest:ci` lifecycle hook and call `create:doc-tests` from the
`build` job before `test:ci`. The hook hid the step from the job log and
made `test:ci` behave differently under npm than when run directly.

CONTRIBUTING.md

@@ -96,8 +96,8 @@ executed test, so a documented example cannot drift from the API. Describe each
 fence with the paragraph directly above it (that text becomes the test title),
 and keep its library import self-contained;
 `npm run create:doc-tests` regenerates, formats and type-checks the tests under
-`src/doc-test/__generated__/`. CI runs it automatically via `pretest:ci`, so run
-it yourself before `npm run verify` when you touched a fence. Why:
+`src/doc-test/__generated__/`. CI runs it in an explicit step before `test:ci`,
+so run it yourself before `npm run verify` when you touched a fence. Why:
 [development/docs.md](./development/docs.md).
 
 ## Code style and formatting