Add manual test for actually-outdated bundle in update flow

[mgoldsborough]

Context

From QA review of issue-37-cli-add-bundle-update-awareness branch.

Problem

The PR test plan has one unchecked item: "Test with an actually outdated bundle (manually downgrade cache metadata)". This is the one scenario that exercises the full happy path end-to-end — detecting an outdated bundle and downloading the update.

Suggested Approach

1. Run mpak run @nimblebraininc/echo to cache the bundle
2. Manually edit ~/.mpak/cache/nimblebraininc-echo/.mpak-meta.json to downgrade the version
3. Run mpak outdated — should list echo as outdated
4. Run mpak update — should download and replace with latest
5. Run mpak outdated — should report all up to date

Could also be captured as an integration test with a mock registry.

Severity

Suggestion — test coverage gap for the primary use case.