Add core app features for event management and notifications

- Add new hook files for departure time, destination station, geocode, theme, walk route, and WienerLinien
- Add navigation types for centralized route definitions
- Update App.tsx to use ref for initialization logic
- Update notification service to use stable exports from expo-notifications
- Remove legacy notifications.ts and rename to expoNotifications.ts
- Add ScrollView to several screens for better layout
- Replace duplicated type definitions with imports from shared navigation types
- Add useTheme to relevant screens
- Remove notification handler duplication in App.tsx

apps/mobile/App.tsx

@@ -1,22 +1,30 @@
-import { useEffect } from 'react';
+import { useEffect, useRef } from 'react';
 import * as Notifications from './src/services/expoNotifications';
 import AppNavigator from './src/navigation/AppNavigator';
 
 export default function App() {
-  useEffect(() => {
-    // Request notification permissions on app start
-    Notifications.requestPermissionsAsync();
+  const initRef = useRef(false);
 
-    // Set up notification handler
-    Notifications.setNotificationHandler({
-      handleNotification: async () => ({
-        shouldShowAlert: true,
-        shouldPlaySound: true,
-        shouldSetBadge: false,
-        shouldShowBanner: true,
-        shouldShowList: true,
-      }),
-    });
+  useEffect(() => {
+    // Run initialization only once
+    if (initRef.current) return;
+    initRef.current = true;
+
+    (async () => {
+      // Request notification permissions
+      await Notifications.requestPermissionsAsync();
+
+      // Set up notification handler (called exactly once)
+      Notifications.setNotificationHandler({
+        handleNotification: async () => ({
+          shouldShowAlert: true,
+          shouldPlaySound: true,
+          shouldSetBadge: false,
+          shouldShowBanner: true,
+          shouldShowList: true,
+        }),
+      });
+    })();
   }, []);
 
   return <AppNavigator />;