Add an Agent Tool ({{ cookiecutter.ai_framework }})

Agent tools live in backend/app/agents/tools/ and are surfaced to the model so it can call them mid-conversation. The assistant is defined in backend/app/agents/.

Steps

1. Write the tool function in backend/app/agents/tools/<tool_name>.py:

   • Async, fully type-hinted, with a clear docstring — the docstring and signature are what the model sees, so make them precise.
   • Pure logic: take typed args, return a JSON-serializable result. Raise on hard errors; return a structured {"error": ...} for soft failures the model should reason about.
   • Keep secrets/IO behind settings and the service layer; don't inline credentials.

2. Export it from backend/app/agents/tools/__init__.py (add the import and append to __all__, matching the existing feature-gated blocks).