fix(path): add Windows validation for Unix-style paths in findNpmDirPathSync

On Windows, Unix-style paths starting with / are not valid and will fail
path operations. Add early return to prevent attempting to resolve these
invalid paths.

This defensive check aligns with the test expectations where Unix paths
return undefined on Windows platforms.

Also updated path examples in comments to use environment variables instead
of hardcoded usernames.

Author: jdalton

packages/cli/src/utils/fs/path-resolve.mts

@@ -50,6 +50,10 @@ export function findBinPathDetailsSync(binName: string): {
 }
 
 export function findNpmDirPathSync(npmBinPath: string): string | undefined {
+  // On Windows, Unix-style paths (starting with /) are not valid.
+  if (WIN32 && npmBinPath.startsWith('/')) {
+    return undefined
+  }
   const MAX_ITERATIONS = 100
   let thePath = npmBinPath
   let iterations = 0
@@ -79,8 +83,8 @@ export function findNpmDirPathSync(npmBinPath: string): string | undefined {
     if (
       // npm bin paths may look like:
       //   /usr/local/share/npm/bin/npm
-      //   /Users/SomeUsername/.nvm/versions/node/vX.X.X/bin/npm
-      //   C:\Users\SomeUsername\AppData\Roaming\npm\bin\npm.cmd
+      //   ~/.nvm/versions/node/vX.X.X/bin/npm
+      //   %USERPROFILE%\AppData\Roaming\npm\bin\npm.cmd
       // OR
       //   C:\Program Files\nodejs\npm.cmd
       //