gh pr create output not captured by command-stream

[konard]

🐛 Bug Description

The output from `gh pr create` command is not properly captured by command-stream, with the PR URL going to stderr instead of stdout, making it difficult to programmatically get the created PR URL.

🔴 Impact

• Can't capture PR URLs programmatically
• Automation scripts can't get PR links
• CI/CD workflows can't report PR URLs

📝 Problem Details

`gh pr create` outputs the PR URL to stderr, but command-stream may not properly capture or distinguish between stdout and stderr.

🔄 Reproduction

```javascript
const result = await $`gh pr create --title "Test" --body "Test PR"`;
console.log(result.stdout); // Empty or incomplete
console.log(result.stderr); // Contains the PR URL
```

🔧 Workaround

Capture both stdout and stderr:
```javascript
const result = await $`gh pr create 2>&1`;
// Or check both result.stdout and result.stderr
```

🔗 References

• Full test: https://github.com/deep-assistant/hive-mind/blob/main/command-stream-issues/issue-11-gh-pr-create-output.mjs