Electron & Qt apps are defaulting to light mode

### What Happened?

Electron apps default to light mode even when the system is set to dark mode.

Zulip renders only the window decorations in light mode, while Signal renders the entire app in light mode.

### Steps to Reproduce

1. Set the system to dark mode.
2. Open an Electron app.

### Expected Behavior

All apps and window decorations appear in dark mode when the system is set to dark mode.

### OS Version

8.x (Circe)

### OS Architecture

amd64 (on most hardwares)

### Session Type

Secure Session (Wayland, This is the default)

### Software Version

Latest release (I have run all updates)

### Log Output

```shell
N/A (it's from multiple apps)
```

### Hardware Info

HP Envy Laptop 16-h1055cl (using Nvidia-610-open)

No source files, tests, or entry points are identified. Reproduce the issue on the listed Wayland setup with an Electron app, then trace how Gala communicates the system color scheme to applications; done means Electron apps and their window decorations follow the system dark-mode setting.

Written by the indexing model from the issue text.