Code Generator modal does not close on Escape while Data Profiler does

## What

The Code Generator modal cannot be closed with Escape. The Data Profiler modal, which uses the same non-Radix shell, had this fixed and handles Escape.

## Where

src/components/CodeGenerator.tsx contains no `Escape` handling and no `onKeyDown` at all.

src/components/DataProfiler.tsx:188-203 documents the same problem being solved for that modal:

```
Escape closes the modal.
...
`ui/dialog`, so nothing bound Escape for it and the header control was the only
exit. Swapping the shell for the Radix primitive would bring Escape along, but
```

So the fix pattern already exists in the repository.

## Expected

Escape closes the Code Generator, the same way it closes the Data Profiler.

## How to fix

Apply the DataProfiler.tsx pattern to CodeGenerator.tsx: mount the key listener only while the modal is open, and unmount it with the modal. Read the comment block at DataProfiler.tsx:188-230 first, it explains why the listener is scoped that way and how it interacts with the shortcuts dialog.

## How to check

Open the Code Generator, press Escape, confirm it closes. Confirm the shortcuts dialog still behaves correctly when both are open.