chore(deps): declare aiohttp and pillow as dev deps

Both were only present transitively (via litellm). Pinning them
explicitly lets us drop the unused LLM tooling from the venv
without breaking tools/loadtest.py or tests/evals/render/render_eval.py.

Author: idank

requirements-dev.txt

@@ -3,3 +3,5 @@ pytest>=9.0.3
 pytest-cov>=7.1.0
 ruff>=0.15.10
 python-dotenv>=1.2.2
+aiohttp>=3.13
+pillow>=12.1