[Bug]: GNOME tray icon is not displayed as a symbolic icon

### ⚠️ Before submitting, please verify the following: ⚠️

- [x] This is a **bug**, not a question or a configuration issue.
- [x] This issue is **not** already reported on Github (I have searched for it).
- [x] Nextcloud Server and Desktop Client are **up to date**. See [Server Maintenance and Release Schedule](https://github.com/nextcloud/server/wiki/Maintenance-and-Release-Schedule) and [Desktop Releases](https://nextcloud.com/install/#install-clients) for supported versions.
- [x] I agree to follow Nextcloud's [Code of Conduct](https://nextcloud.com/contribute/code-of-conduct/)

### Bug description

On GNOME, the Nextcloud tray icon is not displayed as a proper symbolic icon. Instead, it appears as a dark/full-color icon, making it difficult to see in the top panel depending on the panel theme.

This happens even when using GNOME tray extensions configured to display symbolic (monochrome) icons. The desktop client itself works correctly, including status changes, but the tray icon does not follow the GNOME symbolic icon style.

The Fedora package does not appear to ship any symbolic tray icons (e.g. *-symbolic.svg), only regular PNG icons.

### Steps to reproduce

1. Install Fedora Workstation 44 (GNOME).
2. Install the Nextcloud Desktop Client from the Fedora repositories.
3. Install and enable a GNOME tray extension (e.g. Status Tray).
4. Configure the tray extension to use symbolic (monochrome) icons.
5. Start the Nextcloud Desktop Client.
6. Observe the tray icon in the GNOME top panel.

### Expected behavior

The Nextcloud tray icon should use a proper GNOME symbolic icon, matching the appearance of other applications in the GNOME top panel. When a tray extension is configured to display symbolic (monochrome) icons, the Nextcloud icon should also be rendered as a symbolic icon instead of a dark/full-color icon.

### Which files are affected by this bug

No user files are affected. This issue only affects the tray icon displayed by the Nextcloud Desktop Client.

### Operating system

Linux

### Which version of the operating system you are running.

Fedora Linux 44 (GNOME 50)

### Installation method

Distro package manager (please test with the AppImage package ?)

### Nextcloud Server version

31.0.6 Enterprise

### Nextcloud Desktop Client version

4.0.7 daily, fedora

### Did this occur after an update or on a clean installation?

Clean desktop client installation

### Are you using the Nextcloud Server Encryption module?

No

### Are you using an external user-backend?

- [x] Default internal user-backend
- [ ] LDAP or Active Directory
- [ ] SSO - SAML
- [ ] Other

### Nextcloud Server logs

```shell
No relevant server log entries. This issue only affects the Linux desktop client's tray icon.
```

### Additional info

_No response_

No source file or test is named. Start by locating the Linux/GNOME tray-icon entry point and the Fedora package's installed icon assets, then compare them with GNOME's symbolic-icon expectations. Done means the client presents a monochrome symbolic tray icon under the described GNOME configuration while preserving the existing status behavior.

Written by the indexing model from the issue text.