Build a Full-Stack Feature (Practical)

Question

## Problem

Build a small full-stack app/feature: an API endpoint plus a simple UI that lists and creates records (reported Loom 'design a fullstack app').

## Example
```
GET/POST /items + a list UI with optimistic add
```

## Constraints
- Clean separation; error handling

## What Loom looks for
Pragmatic full-stack code, error handling, and async UX — not algorithm tricks.