Add AI options

### ⚠️ 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

Please add the option to enter API let for Gemini and ChatGPT and in settings to customize few most common prompts, then in editing after option to open those prompts. Once text arrives, to have it in separate widget with button to decide if too replace text, add it, or copy it.

### Information

Android version:
Device:
App Version:

### Source

F-Droid

### Format / File type

Not specific

### Additional info / Log

```shell
-
```

Start by mapping the Android settings and editing entry points related to API configuration, prompts, and text replacement. The issue does not name files or tests, so first clarify the supported providers, prompt workflow, response widget behavior, and acceptance criteria before implementation.

Written by the indexing model from the issue text.