Linux desktop integration: set desktopName and fix electron-builder metadata warnings

[regnull]

Goal

Fix the warnings electron-builder prints for the Linux build, so the AppImage links properly with desktop environments.

Context

cd frontend && pnpm electron:package --linux (this also works on macOS) prints:

description is missed in the package.json
author is missed in the package.json
electron uses desktopName as app_id / WM_CLASS for window association. Without it desktop
environments may not link running windows to this .desktop entry. Set desktopName in
package.json and linux.syncDesktopName: true to fix.

Without desktopName, a running OpenBot window may not group with its launcher icon on GNOME and KDE. See electron-builder's Linux docs.

Acceptance criteria

• frontend/package.json has description, author and desktopName
• electron-builder.yml sets linux.syncDesktopName: true
• A Linux build prints none of the three warnings
• Bonus: confirm on a Linux desktop that the window groups with its launcher icon