Fix docs CI: use public npm registry; fix stale path in Makefile

Add .npmrc pinning the project to registry.npmjs.org. The lockfile was
generated from Bloomberg's internal Artifactory mirror, causing npm ci to
crash ("Exit handler never called!") on public GitHub Actions runners that
cannot reach artprod.dev.bloomberg.com. Regenerate package-lock.json
against the public registry.

Also update _docs_conf in the Makefile: antora-worktree-fix.js was
renamed to antora/antora-worktree-fix.js in a previous commit but the
Makefile still referenced the old path, which was why make fell through
to the .DEFAULT cmake-passthrough rule (the file no longer existed at
the expected location).

Co-Authored-By: Claude Sonnet 4.6 (1M context) <noreply@anthropic.com>

Author: steve-downey

.npmrc

@@ -0,0 +1 @@
+registry=https://registry.npmjs.org

Makefile

@@ -256,7 +256,7 @@ clean-tools: ## Remove locally installed documentation tools
 
 realclean: clean-tools clean-docs
 
-_docs_conf  := antora-playbook.yml antora-worktree-fix.js docs/antora.yml docs/mrdocs.yml
+_docs_conf  := antora-playbook.yml antora/antora-worktree-fix.js docs/antora.yml docs/mrdocs.yml
 
 # Docs output lives under the toolchain build path so it uses the same
 # compilation environment as the rest of the build, and the root-level