fix(ci): use gpt-5-mini without openai/ prefix for GitHub Models

GitHub Models expects bare model names (gpt-5-mini), not the
openai/gpt-5-mini format used by OpenRouter.

Co-Authored-By: Claude Opus 4.6 <noreply@anthropic.com>

Author: christso

.github/workflows/evals.yml

@@ -30,7 +30,7 @@ jobs:
         run: |
           cat > .env <<EOF
           GH_MODELS_TOKEN=${{ secrets.GH_MODELS_TOKEN || secrets.GITHUB_TOKEN }}
-          GH_MODELS_MODEL=${{ vars.GH_MODELS_MODEL || 'openai/gpt-5-mini' }}
+          GH_MODELS_MODEL=${{ vars.GH_MODELS_MODEL || 'gpt-5-mini' }}
           COPILOT_MODEL=${{ vars.COPILOT_MODEL || 'gpt-5-mini' }}
           EOF