Update webui-user.bat

[PegasusSpectra]

Description

• change the / for windows users to \\
• the edits ensure the correct directory is found and loaded into the WebUI
• it fixes the WebUI script to find the directory and load the models on the correct directory structure

Screenshots/videos:

Checklist:

• I have read contributing wiki page
• I have performed a self-review of my own code
• My code follows the style guidelines
• My code passes tests

[lllyasviel]

hi we are going to close PRs before forge's recent major revision
if we missed some important PRs, please consider reopen (if that is not already on our todo list