docs(web/guides): address Reviewer A/B consensus findings (round 2)

- Fix stale `box.json` reference at upgrading/index.mdx:28 → `wheels.json`
  (the actual package manifest at the repo root). Round-1 fixed the same
  filename inside changelog.mdx but missed this sibling line in index.mdx;
  Reviewer A flagged it in the round-2 pass and B confirmed.

Signed-off-by: claude[bot] <41898282+claude[bot]@users.noreply.github.com>

Author: github-actions[bot]

web/sites/guides/src/content/docs/v4-0-1-snapshot/upgrading/index.mdx

@@ -25,7 +25,7 @@ Deprecations land in a minor release with a log warning and stay functional unti
 Three sources, in order of authority:
 
 - `vendor/wheels/events/onapplicationstart.cfc` — the `application.$wheels.version` assignment is the runtime truth. As of this snapshot, `4.0.0`.
-- `box.json` at the repo root — the package manifest version.
+- `wheels.json` at the repo root — the package manifest version.
 - `CHANGELOG.md` at the repo root — the most recent non-`[Unreleased]` heading.
 
 If any two disagree, the runtime constant wins — that's the version your app actually boots against.