feat(linux): add --no-tray-icon to hide the tray while keeping the GUI

[RamfiAogusto]

Problem

--no-tray does more than its name suggests. It takes the headless path in main.rs and never starts the iced application:

if args.no_tray {
    // Run headless without UI
    info!("Running in headless mode (no GUI)");

So anything that needs the window becomes unreachable. A BluetoothUIMessage::OpenWindow is still accepted and sent, but there is no consumer on the other end, and the window silently never opens.

That behaviour is correct for a headless run. The gap is that it is the only way to remove the tray icon, so hiding the icon also costs the GUI.

This matters on desktops where a panel indicator already shows battery and listening mode. The tray icon is then redundant, but removing it today means losing the window with it.

Change

--no-tray-icon skips only the tray registration and leaves the GUI running, so the window can still be opened.

--no-tray is untouched and keeps its current headless behaviour.

Testing

Built and run on Ubuntu 26.04, GNOME Shell 50.1 (Wayland), with AirPods Pro 3.

With --no-tray-icon --start-minimized:

• no Running in headless mode line in the log — the GUI is up
• no org.kde.StatusNotifierItem-* name on the session bus — the icon is gone
• an OpenWindow message is both received and consumed, and the window opens

--no-tray was re-checked and still runs headless as before.