desktop app: use a custom user agent string

electron.ts

@@ -26,6 +26,8 @@ electronDl({ saveAs: true });
 // needed for excalidraw export https://github.com/zadam/trilium/issues/4271
 electron.app.commandLine.appendSwitch("enable-experimental-web-platform-features");
 
+electron.app.userAgentFallback = `${electron.app.getName()} ${electron.app.getVersion()}`;
+
 // Quit when all windows are closed, except on macOS. There, it's common
 // for applications and their menu bar to stay active until the user quits
 // explicitly with Cmd + Q.