chore(scripts): remove dead references to a retired repository

Two comments in build-rollup-register.{mjs,test.mjs} used a since-deleted
repository as the example of a nested same-name git repo. Replaced with the
invented `example-repo/example-repo`; the test fixture (`outer/outer`) and
what it proves are unchanged.

Adds scripts/check-retired-refs.mjs (+ test): fails when a tracked text
file names a retired term in its content or path. The term list is
local-only (scripts/retired-terms.local.md, ignored via *.local.md) and
never tracked; a missing or empty list reports NOT CHECKED (exit 2), and
the repo-level test skips with that reason instead of passing silently.
Named exemption list, empty. Chosen *.local.md because the existing ignore
rule already covers it, so .gitignore is untouched.

Red on 69fb250 (112 files, 2 hits, exit 1) -> green (114 files, 0 hits).
Suite 217 -> 227 tests, 211 -> 221 pass; the same 6 check-okf-parity
failures before and after, caused by the worktree path breaking its
sibling-repo lookup (9/9 green in the main checkout). check-versions:
12/12 OK, 0 ERROR.

Co-Authored-By: Claude Opus 5.5 <noreply@anthropic.com>

scripts/build-rollup-register.mjs

@@ -206,7 +206,7 @@ export function buildRegister({ repos }) {
 // state-bearing directories — a fact, not a guarantee, hence the collision gate below.
 //
 // Not descending into a git repo also makes the known nested-name trap
-// (claude-code-100x/claude-code-100x, both git repos) structurally unreachable rather than
+// (e.g. example-repo/example-repo, both git repos) structurally unreachable rather than
 // merely absent.
 //
 // "Is a repo" tests `.git` for EXISTENCE, not directory-ness: a worktree or submodule has