test: cover skillkit package manager discovery

[k4its1t]

Summary

• add parameterized coverage for every static package-manager directory used by skillkit discovery
• cover NVM and mise version directories
• cover pnpm, Yarn, and npm dynamic global-bin fallbacks
• keep the path table synchronized with getPackageManagerBinDirs

Validation

• bun test (31 passed)
• bun run lint
• bun run build
• git diff --check

Closes #42

AI assistance: Codex was used to implement and validate this change.

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