Add prototype structure for banking demo (#1203)

## Summary
- add skeleton `frontend` Next.js app
- add `backend` folder with FastAPI and Agents SDK hooks
- sample env file and script to run both apps
- minimal docs stub

## Testing
- `make format`
- `make lint`
- `make mypy`
- `make tests`


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https://chatgpt.com/codex/tasks/task_i_687ed6408eb4832097d775c4cd4641a2

Author: anurag-openai

.env.example

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+# Environment variables for the demo
+OPENAI_API_KEY=

backend/.gitignore

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+__pycache__
+*.pyc

backend/README.md

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+# Backend
+
+This folder contains the Python backend using FastAPI and the OpenAI Agents SDK.
+Run `uvicorn backend.main:app --reload` to start the development server.

backend/__init__.py

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+from fastapi import FastAPI
+
+app = FastAPI()
+
+
+@app.get("/health")
+def health() -> dict[str, str]:
+    return {"status": "ok"}

backend/main.py

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+[project]
+name = "banking-backend"
+version = "0.1.0"
+requires-python = ">=3.11"
+dependencies = [
+    "fastapi",
+    "uvicorn",
+    "openai",
+]
+
+[tool.ruff]
+line-length = 88

backend/pyproject.toml

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+from fastapi.testclient import TestClient
+from backend.main import app
+
+
+def test_health() -> None:
+    client = TestClient(app)
+    response = client.get("/health")
+    assert response.status_code == 200
+    assert response.json() == {"status": "ok"}

backend/tests/test_main.py

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+# Agentic Private Banker Demo
+
+This document provides a high-level overview of the multi-agent banking prototype.

docs/banking-demo.md

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+node_modules
+.next
+out

frontend/.gitignore

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+# Frontend
+
+This folder contains the NextJS frontend for the Agentic Private Banker demo.
+Run `npm install` and `npm run dev` to start the development server.