Build initial logic skeleton benchmark

.env.example

@@ -0,0 +1,14 @@
+# Shared fallback. Store the real value as a Gitea Actions secret, never here.
+OPENAI_API_KEY=
+OPENAI_BASE_URL=https://api.openai.com/v1
+
+# Renderer and solver can use different OpenAI-compatible providers/models.
+RENDERER_API_KEY=
+RENDERER_BASE_URL=
+RENDERER_API_STYLE=responses
+RENDERER_MODEL=
+
+SOLVER_API_KEY=
+SOLVER_BASE_URL=
+SOLVER_API_STYLE=responses
+SOLVER_MODEL=