Merge branch 'Three_files'

sizing interface

updated to allow 3 files at once and load sample stls

Change black as material and white as empty space

Fix Hugging Face Spaces startup

Shorten Hugging Face Space description

Added requirements.txt from uv.lock and Hugging Face Spaces frontmatter to README.md

Simplify STL viewer layout

Merge pull request #1 from MichaelRKessler/codex/gradio-stl-tiff-slicer

Add Gradio STL slicer app

Add project instructions