Event ID is `undefined` in `missing` trigger

Nobody has claimed this yet.

### Description

The event ID is always being passed properly to the `missing` trigger. In our error logging we are finding that the ID property is missing, suggesting that it is `undefined` when the `missing` trigger is activated. I could not find any issues describing this nor any part of the [documentation](https://github.com/lingui/js-lingui/blob/main/website/docs/ref/core.md#missing) that explains how this could happen or what to do when it does

### Verifications

- [x] I've checked [the docs](https://lingui.dev) and this isn't covered there.
- [x] I've searched existing issues on [GitHub](https://github.com/lingui/js-lingui/issues).

### Reproduction Steps

```tsx
import { I18nProvider } from '@lingui/react';
import { i18n, Locale } from '@lingui/core';

type MissingMessageEvent = {
locale: Locale;
id: string;
};

function onMissingTranslation(event: MissingMessageEvent) {
// Note: id is undefined here so it is not being picked up in the console, as stringify drops undefined values
console.error(`Missing translation for string: ${JSON.stringify(event)}`)
}

export default function App({
children
}: {
children: React.ReactNode;
}) {
const locale = "en-US"; // example
const messages = loadMessages(...); // queried using a suspense query

const activatedI18n = useMemo(() => {
i18n.load(locale, messages);
i18n.activate(locale);
i18n.on('missing', onMissingTranslation);
return i18n;
}, [locale, messages]);

return {children};
}
```

### Expected Behavior

I would expect that `id` is a present field in our console errors.

### Macro Support

SWC with @lingui/swc-plugin

### Lingui Version

5.0.0-next.0

### Babel Version

_No response_

### Framework

Next.js

Start with the `missing` trigger documentation in the linked core reference and the provided Next.js reproduction. Trace how the event is emitted and compare the observed payload with the expected `id` field. Done means the cause and expected behavior are verified, with the resolution reflected in coverage or documentation.

Written by the indexing model from the issue text.