[BUG] JSX comments crash inside fragments

When adding a comment as a child of a fragment, it suddenly breaks things:

```tsx
import { Component } from "@geajs/core";
import type { JSX } from "@geajs/core/jsx-runtime";

export type FooButtonProps = JSX.IntrinsicElements["button"];

export class FooButton extends Component {
template({ children, class: cls, ...props }: FooButtonProps) {
return (
<>
{/* */}

{children}


);
}
}
```

// throws
// Uncaught TypeError: Cannot read properties of undefined (reading 'firstChild')

Start by running the supplied TSX reproduction in the JSX transform and DOM patching paths, then trace the fragment comment case to the undefined value whose firstChild access fails. Done means a JSX comment can appear as a fragment child without throwing while the surrounding button still renders correctly.

Written by the indexing model from the issue text.