fix: Avoid pnpm batch-shim shutdown hangs on Windows

[sahyl]

Fixes #14803.

Persistent tasks can hang after Ctrl+C when pnpm is installed through npm on Windows. The app exits, but pnpm.cmd stays alive waiting for batch-job confirmation.

Recognize npm’s native pnpm launcher and run its pnpm.exe directly. Compare the complete shim against the embedded npm-generated fixture before bypassing it so Corepack keeps control of version selection. Existing global-store support remains unchanged.

Add Windows regression tests for npm and Corepack shims, unreadable or modified scripts, paths with spaces, and shim-name casing.

Validation

• 14 Windows unit tests passed. LF and CRLF coverage now runs through command selection.
• Native Windows CLI checks confirmed shutdown, argument forwarding, and Corepack version selection.
• Formatting, Clippy, and diff checks passed.

Unrecognized shim templates keep their existing behavior and may still need a second Ctrl+C. Corepack 0.31.0’s wrapper requires a second Ctrl+C on both main and this branch.

The original checks used Windows GNU builds and generated layout fixtures. Additional verification used Windows 11 ARM64 MSVC on a clean NTFS checkout. It used an actual npm-generated pnpm 12.6.0 shim in a prefix containing spaces, without an adjacent node.exe. One Ctrl+C exited with code 0 and preserved quoted arguments. The directory-fallback test failed as expected when is_file() was temporarily weakened to exists(). A default Node installer setup has not been tested.

[vercel]

@sahyl is attempting to deploy a commit to the Internal Apps Team on Vercel.

A member of the Team first needs to authorize it.

[anthonyshew]

Thanks. I did some simplifying and tested that it still works.