fix: handle monitor hotplug for greeter windows (v0.8.2)

Greeter windows were only created at startup. Hotplugged monitors (e.g.
HDMI reconnect) would show no UI. Connect to the monitor ListModel's
items-changed signal to create greeter windows for newly added monitors.

Aligned with moonlock's hotplug fix using the same pattern adapted for
gtk4-layer-shell (ListModel) instead of session-lock (connect_monitor).

src/main.rs

@@ -11,9 +11,11 @@ mod sessions;
 mod users;
 
 use gdk4 as gdk;
+use glib::clone;
 use gtk4::prelude::*;
 use gtk4::{self as gtk, gio};
 use gtk4_layer_shell::LayerShell;
+use std::rc::Rc;
 fn load_css(display: &gdk::Display) {
     let css_provider = gtk::CssProvider::new();
     css_provider.load_from_resource("/dev/moonarch/moongreet/style.css");
@@ -80,6 +82,33 @@ fn activate(app: &gtk::Application) {
                 first = false;
             }
         }
+
+        // Handle monitor hotplug — create greeter windows for newly added monitors
+        // (without keyboard, since the primary monitor already has it)
+        let bg_texture = Rc::new(bg_texture);
+        let config = Rc::new(config);
+        monitors.connect_items_changed(clone!(
+            #[weak]
+            app,
+            #[strong]
+            blur_cache,
+            move |list, position, _removed, added| {
+                for i in position..position + added {
+                    if let Some(monitor) = list
+                        .item(i)
+                        .and_then(|obj| obj.downcast::<gdk::Monitor>().ok())
+                    {
+                        log::debug!("Monitor hotplug: creating greeter window");
+                        let window = greeter::create_greeter_window(
+                            bg_texture.as_ref().as_ref(), &config, &blur_cache, &app,
+                        );
+                        setup_layer_shell(&window, false, gtk4_layer_shell::Layer::Top);
+                        window.set_monitor(Some(&monitor));
+                        window.present();
+                    }
+                }
+            }
+        ));
     } else {
         // No layer shell — single window for development
         let greeter_window = greeter::create_greeter_window(bg_texture.as_ref(), &config, &blur_cache, app);