Pinned header in the UI

### Prerequisites

- [X] I have checked the [Wiki](https://github.com/AdguardTeam/AdGuardHome/wiki) and [Discussions](https://github.com/AdguardTeam/AdGuardHome/discussions) and found no answer

- [X] I have searched other issues and found no duplicates

- [X] I want to request a feature or enhancement and not ask a question

### The problem

Beim Scrollen verschwindet die Kopfzeile nach oben aus dem Sichtfeld, was störend ist.

### Proposed solution

Kopfzeile im Theme festtackern

### Alternatives considered and additional information

_No response_