[Bug]: Account details flyout does not open (blank) in new 34.0.0 tray menu

### ⚠️ 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've searched it).
- [X] Nextcloud Server and Desktop Client are **up to date**.
- [X] I agree to follow Nextcloud's Code of Conduct.

### Bug description

After upgrading from 33.0.7 to 34.0.0 (new tray/menu redesign from #10164), clicking the tray icon shows the account entry ("Firstname Lastname (server.url)") with an expand arrow (`>`) on the right. Clicking that arrow does nothing: no submenu, no sync status, no folder list appears. The rest of the menu (Aggiungi account / Impostazioni / Quit) renders and works fine. Only the account-details expansion is blank/non-functional.

Sync itself works correctly in the background (confirmed via logs — folders sync successfully), so this is purely a UI/rendering issue in the new tray menu.

### Steps to reproduce

1. Run the official `Nextcloud-34.0.0-x86_64.AppImage` on Fedora 44, GNOME (Wayland session, client running via XWayland/xcb — no wayland platform plugin bundled in this AppImage)
2. Click the tray icon to open the menu
3. Click the `>` arrow next to the account name
4. Nothing happens — no submenu/details panel opens

### Expected behavior

Clicking the account expand arrow should show account/sync details (as in the pre-34 client, or as shown in the redesign screenshots in #10164).

### Environment

- **OS**: Fedora Linux 44 (Workstation Edition)
- **Desktop environment**: GNOME, Wayland session (client itself runs via XWayland, `xcb` Qt platform plugin — no `wayland` plugin available in this AppImage build)
- **GPU**: Intel Iris Xe Graphics (Raptor Lake-P, integrated)
- **Nextcloud Desktop Client**: 34.0.0 (build 40916), official AppImage
- **Kernel**: 7.1.4-204.fc44.x86_64

### Workarounds tried (no effect)

- `QT_QUICK_BACKEND=software` — same blank result
- `QT_QPA_PLATFORM=wayland` — fails entirely, AppImage has no bundled wayland plugin (`Available platform plugins are: xcb.`)

### Additional context

Possibly related to the tray redesign in #10164 (merged 2026-07-08) and to prior XWayland-rendering issues such as #10338.