Show search as find in page, not in a popup

### ⚠️ This issue respects the following points: ⚠️

- [X] This is a **enhancement/feature request**. Not a [bug or question](https://github.com/gsantner/markor/issues/new/choose).
- [X] The topic is **not** already reported at [Issues](https://github.com/gsantner/markor/issues?q=#js-issues-search). _(I've searched it)_.
- [X] Markor **is** up to date. See [Releases](https://github.com/gsantner/markor/tags) for the latest version. Updates are available from [F-Droid](https://f-droid.org/en/packages/net.gsantner.markor/) and GitHub.
- [X] The wanted feature/enhancement is not present in the latest development version (git master). (Please [download](https://nightly.link/gsantner/markor/workflows/build-android-project/master) and try the test version of Markor, named **Marder**. Don't worry; Markor and Marder appear as completely separate applications. You can install both side-by-side, and Markor's settings are not touched. If your desired feature is present, you don't need to open this issue. The change will be part of the next Markor update.)

### Description

Currently:

1. search term is lost when selecting a result line.
2. you can't see results in context (within preceding/succeeding lines).

Both should improve if it is shown as a browser find in page feature that preserves the search query.

The current popup can still be accessible though a button or so.

### Information

App Version: 2.11.1

### Source

F-Droid

### Format / File type

Not specific

### Additional info / Log

_No response_

The issue names no files or tests; start by locating the current search popup and the flow used when selecting a result line. Compare that flow with the requested find-in-page behavior, then verify that the query is preserved, surrounding lines remain visible, and the existing popup remains accessible.

Written by the indexing model from the issue text.