Build a minimal full‑stack app for monetary transactions

Objective

Implement a minimal full‑stack web application that supports basic monetary transactions and account balances.

Requirements

• Backend API
  • Expose a REST or GraphQL API (choose one) to:
    1. Create accounts.
    2. Create transactions (credit or debit) against an account.
    3. Retrieve accounts and transactions.
• Data persistence
  • In‑memory store or a lightweight database is acceptable.
• Frontend
  • A simple page to:
    1. Create an account.
    2. Submit a credit or debit transaction.
    3. View the current balance and recent transactions.
• Validation and rules
  • Validate inputs (e.g., non‑negative amounts with up to 2 decimal places, required fields).
  • Prevent negative balances (reject debits that would drive the balance below zero).
• Tests
  • Include basic automated tests covering happy paths and error cases.
• Developer experience
  • Provide setup instructions and a concise README.

Deliverables

• Source code for backend and frontend.
• Tests and instructions to run them.
• README with how to run, API summary, and any assumptions.

Notes

• Focus on correctness and clarity over breadth.
• Handling money precisely is important; avoid floating‑point errors.
• Keep the UI minimal; functionality matters more than styling.