fix: normalize WSL Windows mount paths

[mmhh256]

Summary

• recognize /mnt/<drive> paths as Windows-backed WSL mount paths
• compare those paths and their basenames case-insensitively
• preserve case-sensitive comparison for regular POSIX paths
• add regression coverage for the session cwd reported in cwd normalisation from #377 misses WSL /mnt/<drive> paths, so session/list cannot find sessions it just created #431

Fixes #431

Testing

• npm exec -- vitest run src/__tests__/PathUtils.test.ts --no-file-parallelism
• npm run typecheck
• npm run build