Fix imported presets not persisting, remove duplicate help handler

pixstrip-gtk/src/app.rs

@@ -1990,6 +1990,7 @@ fn import_preset(window: &adw::ApplicationWindow, ui: &WizardUi) {
             match store.import_from_file(&path) {
                 Ok(preset) => {
                     let msg = format!("Imported preset: {}", preset.name);
+                    let _ = store.save(&preset);
                     let toast = adw::Toast::new(&msg);
                     ui.toast_overlay.add_toast(toast);
                 }