normalize_path() unconditionally converted Windows paths like
C:\Users\... to WSL format /mnt/c/Users/..., which breaks path
resolution on native Windows. This caused LM Studio GGUF models
to fail detection (detect_gguf_model returned None for the invalid
path), falling through to the Unsloth import path which requires
a GPU.
Now only performs the /mnt/ mapping when actually running under WSL.
On native Windows, drive letters are preserved and backslashes are
normalized to forward slashes.