feat: expose a mobile sidebar-apps selector for the drawer

src/lib/sidebar-apps.ts

@@ -0,0 +1,23 @@
+import { Linking } from 'react-native';
+import { useSettingsStore, type SidebarApp } from '../stores/settings-store';
+
+/**
+ * Sidebar apps the user marked "show on mobile". The drawer (SidebarDrawer)
+ * is expected to render these below the folder list; the settings pane only
+ * edits them. Mirrors the webmail's navigation-rail filter on `showOnMobile`.
+ */
+export function useMobileSidebarApps(): SidebarApp[] {
+  return useSettingsStore((s) => s.sidebarApps.filter((app) => app.showOnMobile));
+}
+
+/**
+ * Open a sidebar app. Inline (iframe) apps have no native equivalent yet, so
+ * both open modes hand the URL to the system browser.
+ */
+export async function openSidebarApp(app: SidebarApp): Promise<void> {
+  try {
+    await Linking.openURL(app.url);
+  } catch {
+    // unsupported scheme - nothing to do
+  }
+}