Berd 0.6.2 on Windows agent-setup cursor-agent: curl

### Before filing

- [x] I searched [open and closed issues](https://github.com/block/berd/issues?q=is%3Aissue) for duplicates.
- [x] I reproduced this on the [latest release](https://github.com/block/berd/releases).
- [x] This is one bug, not several bundled together.

### Closest existing issue

1

### What's broken

Berd 0.6.2 on Windows
agent-setup cursor-agent:
curl -fsSL https://cursor.com/install | bash
Failed to run command: The system cannot find the path specified. (os error 3)

### Steps to reproduce

1. Launch Berd
2.
3.

### What you expected to happen

Berd 0.6.2 on Windows
agent-setup cursor-agent:
curl -fsSL https://cursor.com/install | bash
Failed to run command: The system cannot find the path specified. (os error 3)

### What actually happened

Berd 0.6.2 on Windows
agent-setup cursor-agent:
curl -fsSL https://cursor.com/install | bash
Failed to run command: The system cannot find the path specified. (os error 3)

### How often does it happen?

Every time — reliably reproducible

### Berd version

Berd 0.6.2 on Windows

### Operating system

Windows

### Model and provider

Cursor Agent

### Relevant log output

```text
Cursor Agent
```

### Screenshots, recordings, or other context

Berd 0.6.2 on Windows
agent-setup cursor-agent:
curl -fsSL https://cursor.com/install | bash
Failed to run command: The system cannot find the path specified. (os error 3)

Start by reproducing the `agent-setup cursor-agent` flow on Windows and inspect the entry point that runs `curl -fsSL https://cursor.com/install | bash`. Compare the command execution path with Windows requirements; done means Cursor Agent setup completes successfully on Windows or reports a clear supported-platform error.

Written by the indexing model from the issue text.