feat: show greeter UI on all monitors, not just one (v0.8.0)

Wayland surfaces belong to exactly one output — mirroring is not an option.
Create one full greeter window per monitor via set_monitor(), with only the
first receiving KeyboardMode::Exclusive. Removes the old wallpaper-only
secondary windows. Matches moonlock's per-monitor pattern.

src/main.rs

@@ -63,30 +63,27 @@ fn activate(app: &gtk::Application) {
     let use_layer_shell = std::env::var("MOONGREET_NO_LAYER_SHELL").is_err();
     log::debug!("Layer shell: {use_layer_shell}");
 
-    // Main greeter window (login UI) — compositor picks focused monitor
-    let greeter_window = greeter::create_greeter_window(bg_texture.as_ref(), &config, &blur_cache, app);
     if use_layer_shell {
-        setup_layer_shell(&greeter_window, true, gtk4_layer_shell::Layer::Top);
-    }
-    greeter_window.present();
-
-    // Wallpaper-only windows on all monitors (only with layer shell)
-    if use_layer_shell
-        && let Some(ref texture) = bg_texture
-    {
+        // One greeter window per monitor — only the first gets keyboard input
         let monitors = display.monitors();
         log::debug!("Monitor count: {}", monitors.n_items());
+        let mut first = true;
         for i in 0..monitors.n_items() {
             if let Some(monitor) = monitors
                 .item(i)
                 .and_then(|obj| obj.downcast::<gdk::Monitor>().ok())
             {
-                let wallpaper = greeter::create_wallpaper_window(texture, config.background_blur, &blur_cache, app);
-                setup_layer_shell(&wallpaper, false, gtk4_layer_shell::Layer::Bottom);
-                wallpaper.set_monitor(Some(&monitor));
-                wallpaper.present();
+                let window = greeter::create_greeter_window(bg_texture.as_ref(), &config, &blur_cache, app);
+                setup_layer_shell(&window, first, gtk4_layer_shell::Layer::Top);
+                window.set_monitor(Some(&monitor));
+                window.present();
+                first = false;
             }
         }
+    } else {
+        // No layer shell — single window for development
+        let greeter_window = greeter::create_greeter_window(bg_texture.as_ref(), &config, &blur_cache, app);
+        greeter_window.present();
     }
 }