Add prototype structure for banking demo (#1205)

## Summary
- create `test_repo` folder with skeleton demo structure
- include backend FastAPI stub, frontend Next.js stub, docs, and
utilities
- add example tests and env file

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


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

Author: anurag-openai

test_repo/.env.example

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+# Example environment variables.
+OPENAI_API_KEY=your-key-here
+BACKEND_URL=http://localhost:8000

test_repo/__init__.py

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+__pycache__
+*.pyc
+.env

test_repo/backend/.gitignore

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+# Backend
+
+This folder contains the FastAPI backend for the banking demo.

test_repo/backend/README.md

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

test_repo/backend/__init__.py

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+[project]
+name = "banking-demo-backend"
+version = "0.1.0"
+dependencies = [
+    "fastapi",
+    "uvicorn",
+    "openai",
+]

test_repo/backend/main.py

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

test_repo/backend/pyproject.toml

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+# Banking Demo Prototype
+
+This document outlines the high-level structure for the banking demo prototype.

test_repo/backend/tests/test_demo_main.py

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+node_modules
+.next
+out