[Bug]: No in-page text search in HTML maximized preview

### Deployment type

Official App

### What happened?

When I maximize the HTML preview of a comment on an issue page, I would like to still be able to use the Ctrl+F or Command+F in-page search function, but it currently doesn't seem to be supported.

I understand that HTML preview is a key scenario for displaying content. Given the large amount of information involved, it is important to extend the in-page search functionality to the HTML preview state as well.

### Steps to reproduce

1. Find an issue page containing HTML.
2. Click the HTML preview button, which will expand the HTML into a separate page.
3. Use the Ctrl+F or Command+F shortcut. You will notice that the in-page search box does not pop up.

### Screenshots (optional)

_No response_

### Additional context (optional)

```shell
multica: v0.3.43
```

Start by reproducing the issue from an issue page containing HTML, then inspect the HTML preview entry point and its maximized separate-page state. Done means Ctrl+F or Command+F opens the browser's in-page search while the maximized preview is displayed and can find its text.

Written by the indexing model from the issue text.