Fix npm update prefix for symlinked bins

[w287346141]

Summary

• resolve symlinked npm bin paths before extracting the global install prefix
• keep synthetic/nonexistent test paths working by falling back to the literal path
• add a regression test covering a real bin symlink layout

Validation

• npm.cmd test -- --run tests/version.test.ts tests/startup-update-check.test.ts
• npm.cmd run lint
• npm.cmd run typecheck
• git diff --check
• push hook ran npm.cmd run verify