fix(desktop): set the main window icon on Linux

On X11/XWayland (Electron's default on Wayland sessions) the window had no
icon, so KDE Plasma showed the generic placeholder. Point BrowserWindow at
the packaged icon.png so the compositor has an icon to render.

desktop/main.js

@@ -241,6 +241,11 @@ function createMainWindow() {
 	mainWindow = new BrowserWindow({
 		width: 1680,
 		height: 960,
+		// Without an explicit window icon, X11/XWayland compositors (e.g. KDE
+		// Plasma) fall back to a generic placeholder when WM_CLASS doesn't match
+		// an installed .desktop file. icon.png lives at the app root because
+		// build/ is electron-builder's buildResources dir and isn't packaged.
+		icon: path.join(__dirname, 'icon.png'),
 		webPreferences: {
 			...BASE_WEB_PREFERENCES,
 			preload: path.join(__dirname, 'preload.js'),