Improve screen reader support for wizard navigation

- Announce step number and name when navigating between steps
- Add accessible label to batch queue toggle button
- Add accessible label to navigation view with shortcut hint
- Step transitions update accessible property for screen readers

pixstrip-gtk/src/app.rs

@@ -389,6 +389,9 @@ fn build_ui(app: &adw::Application) {
         .visible(false)
         .build();
     queue_button.add_css_class("flat");
+    queue_button.update_property(&[
+        gtk::accessible::Property::Label("Toggle batch queue panel"),
+    ]);
     header.pack_start(&queue_button);
 
     // Help button for per-step contextual help
@@ -415,6 +418,9 @@ fn build_ui(app: &adw::Application) {
     // Navigation view for wizard content
     let nav_view = adw::NavigationView::new();
     nav_view.set_vexpand(true);
+    nav_view.update_property(&[
+        gtk::accessible::Property::Label("Wizard steps. Use Alt+Left/Right to navigate."),
+    ]);
 
     // Build wizard pages
     let pages = crate::wizard::build_wizard_pages(&app_state);
@@ -958,6 +964,15 @@ fn navigate_to_step(ui: &WizardUi, target: usize) {
         ui.nav_view.replace(&ui.pages[..=target]);
         ui.title.set_subtitle(&ui.pages[target].title());
 
+        // Announce step change for screen readers
+        let step_name = ui.pages[target].title().to_string();
+        let total_steps = ui.pages.len();
+        ui.nav_view.update_property(&[
+            gtk::accessible::Property::Label(
+                &format!("Step {} of {}: {}", target + 1, total_steps, step_name)
+            ),
+        ]);
+
         // Focus management - move focus to first interactive element on new step
         // Use idle callback to let the page fully render first
         let page = ui.pages[target].clone();