Option to Show First Few Lines of File in File Browser

### ⚠️ 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

On my PC, my note-taking system creates files with names based on ID. This is useful as it allows me to create notes very quickly but it makes things a little harder to locate once they are synced to to my phone.

It would be nice if the file browser view allowed the option of showing the first `x` number of lines/bytes/whatever of the file so you can get the gist of what it contains.

### Information

Android version: 15
Device: Pixel 6
App Version: 2.14.1 (158)

### Source

F-Droid

### Format / File type

Not specific

### Additional info / Log

```shell
-
```

Start by locating Markor’s file browser entry point and inspecting how files are listed. Clarify whether the preview uses lines or bytes, its configurable limit, and how it appears in the list; done means the option is available and previews are visible without opening files. No source path or test is named, so repository exploration is required.

Written by the indexing model from the issue text.