[Bug]: On KDE, client and server side decoration are displayed together

### Pre-flight checklist

- [x] I searched [existing issues](https://github.com/AprilNEA/OpenLogi/issues?q=is%3Aissue) and this is not a duplicate.
- [x] I am on the [latest release](https://github.com/AprilNEA/OpenLogi/releases/latest) or a recent `master` build.
- [x] I quit **Logi Options+** before running OpenLogi (the two apps fight over HID++ access and only one can own a receiver at a time).

### Which part of OpenLogi?

GUI (desktop app)

### OpenLogi version

0.7.10

### Operating system

Linux

### OS version & architecture

KDE Neon 24.04

### Device model

MX Keys S, MX Master 3S

### How is the device connected?

Logi Bolt receiver

### Affected area(s)

- [ ] Device discovery / detection
- [ ] Button remapping
- [ ] DPI control
- [ ] SmartShift
- [ ] Per-application profiles
- [ ] Battery status
- [ ] Settings / configuration (TOML)
- [ ] Auto-update
- [ ] Menu bar / tray
- [x] Other

### What happened?

The server side window decoration (I assume this is the default with kWin) and client side decoration are both visible.

An option to select what decoration type the user prefers would be nice. The other type should then be disabled.

### Steps to reproduce

1. Open OpenLogi on KDE

### Diagnostics report

```markdown

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### `openlogi list` output

```text

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### Logs

```shell

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### macOS permissions (if applicable)

- [ ] OpenLogi has **Accessibility** permission (needed to remap buttons via the event tap).
- [ ] OpenLogi has **Input Monitoring** permission (needed for Bluetooth-direct devices and capture).

No source files, tests, or entry points are named in the issue. Reproduce the window on KDE Neon 24.04 and inspect the desktop GUI window-decoration setup; done means only one decoration type is visible, with the user's preferred type respected if an option is added.

Written by the indexing model from the issue text.