feat(gui): wire adw::ToastOverlay for error surfacing

gui/src/keys_page.rs

@@ -12,14 +12,16 @@ pub(crate) struct KeysPage {
     pub root: adw::Bin,
     daemon: Rc<RefCell<Option<Daemon>>>,
     parent_window: gtk::Window,
+    toast_overlay: adw::ToastOverlay,
 }
 
 impl KeysPage {
-    pub fn new(parent_window: gtk::Window) -> Rc<Self> {
+    pub fn new(parent_window: gtk::Window, toast_overlay: adw::ToastOverlay) -> Rc<Self> {
         let page = Rc::new(Self {
             root: adw::Bin::new(),
             daemon: Rc::new(RefCell::new(None)),
             parent_window,
+            toast_overlay,
         });
         let p = page.clone();
         glib::MainContext::default().spawn_local(async move {
@@ -165,9 +167,8 @@ impl KeysPage {
     }
 
     fn show_toast(self: &Rc<Self>, msg: &str) {
-        // ToastOverlay wiring lands in Task 7. Until then write to stderr so
-        // manual smoke can observe what would be shown.
-        eprintln!("[gui toast] {msg}");
+        let toast = adw::Toast::builder().title(msg).timeout(5).build();
+        self.toast_overlay.add_toast(toast);
     }
 }