Edge PWAs no longer use separate window class - all group under main Edge icon (Wayland / GNOME)

### Description
Hi, and thank you for maintaining this Flatpak.
It’s been working really well overall.

I’ve recently noticed a change in behavior starting around **2025-09-07 to 2025-09-10**: all **installed PWAs (even across different profiles)** now appear grouped under the **main Edge browser icon** in the GNOME Shell dash/taskbar when using the **Flatpak version of Edge on Wayland**.

Previously, each PWA would open in its **own window group with its own icon**. This still works on Chromium/Brave/Chrome on the same system, and can still be restored there by editing the `.desktop` file to include:

`StartupWMClass=`

In the current Edge Flatpak build, this no longer has any effect, which makes it harder to use PWAs separately in workspaces or for task switching. This might be related to how the `.desktop` files or `StartupWMClass` values are being handled in the Flatpak packaging.

---

### Environment
- Package: com.microsoft.Edge (Flatpak)
- OS: Ubuntu 25.04 x86_64
- Kernel: Linux 6.14.0-29-generic
- DE: GNOME 48.0
- WM: Mutter (Wayland)
- GPU: Intel Iris Xe
- CPU: 13th Gen Intel Core i5-1340P

---

### Steps to Reproduce
1. Install any PWA (e.g. Outlook, Teams, Spotify) from Edge (Flatpak)
2. Launch the installed PWA
3. Observe that it appears grouped under the main Edge browser icon

---

### Expected Behavior
- PWAs should appear as their **own app icon/window group** like they did previously (and as they still do in Chromium-based browsers)

---

### Actual Behavior
- All PWAs are now bundled under the main Edge icon/window group
- Editing the generated `.desktop` files to add `StartupWMClass` no longer changes the behavior

---

### Notes
- The change appeared between **2025-09-07 and 2025-09-10**
- It does not occur in Chromium, Brave, or Chrome on the same system
- It might be related to `.desktop` file handling or `StartupWMClass` behavior within the Flatpak sandbox

Thank you for your time and work.
This package has been great overall, and I appreciate your efforts to maintain it!