Highlight Theme 3.1 + Scaler sub-theme fit, promote GRPO results section

Fix: use raw GitHub URL for chart image to bypass CDN cache

Update: replace broken chart with winning GRPO results (Overall 0.29->0.57)

Fix: add gradio to pyproject.toml deps, update README structure to match actual files

Professional README in OpenEnv style

Add openenv tag and full README content

Initial commit