Fade login handoff through black, spinner while authenticating

Co-Authored-By: Claude Opus 5.5 <noreply@anthropic.com>

settings/quickshell/AuthView.qml

@@ -194,6 +194,23 @@ Item {
                 Keys.onEscapePressed: text = ""
             }
 
+            // Spinner while PAM checks the password (and, in the greeter,
+            // through the fade-out into the session).
+            Text {
+                anchors.centerIn: parent
+                visible: view.busy
+                text: "loader-circle"
+                font.family: view.theme.iconFont
+                font.pixelSize: 20
+                color: view.theme.accent
+                RotationAnimation on rotation {
+                    running: view.busy
+                    from: 0; to: 360
+                    duration: 900
+                    loops: Animation.Infinite
+                }
+            }
+
             // Visible confirm button (after TextInput: on top)
             Rectangle {
                 anchors.right: parent.right