fix(server): keep mise-owned npm packages manual-only - #9927

Eligibility
This is a narrowly scoped server bug fix that prevents mise-owned non-Node packages from being offered an incorrect npm updater while preserving ordinary and mise-Node npm updates. Regression tests cover the changed and preserved behaviors, with no product-default or static-analysis configuration changes.

Notes:
No code owners found in target merge base df8e0eb