[CalvinAllen]

Summary

Installing any runtime failed when the dtvem root is on a different drive than the OS temp directory (e.g. DTVEM_ROOT=H:\SDKs\dtvem with Windows on C:):

✗ failed to move to install location: rename C:\Users\user\AppData\Local\Temp\dtvem-node-24.22.0\extracted H:\SDKs\dtven\versions\node\24.22.0: The system cannot move the file to a different disk drive.

All three providers downloaded and extracted into os.TempDir() and then os.Renamed the result into versions/. os.Rename can't move a directory across volumes on Windows, or across filesystems on Unix (so a tmpfs-backed /tmp has the same failure).

Changes

• 📁 config.Paths gains Temp (<root>/tmp), plus StagingPath(runtime, version) and CreateStagingDir(runtime, version).
• 🔀 Node, Python and Ruby installs stage in <root>/tmp/<runtime>-<version>, so the final move is always a same-volume rename (still atomic, no copying).
• 🧹 CreateStagingDir clears leftovers from an interrupted install before reuse, since the OS temp cleaner no longer covers this location. The existing deferred cleanup still removes the staging dir after each install.

Testing

• ✅ New tests in internal/config/paths_test.go: staging path layout, same volume as versions/, not inside versions/, directory creation, and stale-leftover removal.
• ✅ ./rnr check passes; go vet and go test ./... also pass in a clean worktree of this commit alone.
• ✅ End-to-end on Windows with a scratch DTVEM_ROOT: dtvem install node 24.22.0 staged under <root>\tmp, installed, node --version reports v24.22.0, and tmp\ was left empty.
• ⚠️ Not reproduced on a real second drive: the only other drive on the dev machine is a Google Drive mount.

Resolves #278

[CalvinAllen]

Superseded by 83a3ecf. This commit was squash-merged into main as part of #280, and the five files are identical to what's here, so this PR has nothing left to merge. Closing.