quite a few UX improvements

frontend/lib/pages/new_trip_preferences.dart

@@ -1,5 +1,6 @@
 import 'package:anyway/layouts/scaffold.dart';
 import 'package:anyway/modules/new_trip_button.dart';
+import 'package:anyway/structs/landmark.dart';
 import 'package:anyway/structs/preferences.dart';
 import 'package:anyway/structs/trip.dart';
 import 'package:flutter/cupertino.dart';
@@ -20,6 +21,14 @@ class _NewTripPreferencesPageState extends State<NewTripPreferencesPage> with Sc
 
   @override
   Widget build(BuildContext context) {
+    // Ensure that the trip is "empty" save for the start landmark
+    // This is necessary because users can swipe back to this page even after the trip has been created
+    if (widget.trip.landmarks.length > 1) {
+      Landmark start = widget.trip.landmarks.first;
+      widget.trip.landmarks.clear();
+      widget.trip.addLandmark(start);
+    }
+
     return mainScaffold(
       context,
       child: Scaffold(

frontend/lib/pages/no_trips_page.dart

@@ -0,0 +1,50 @@
+import 'package:anyway/pages/new_trip_location.dart';
+import 'package:flutter/material.dart';
+
+import 'package:anyway/layouts/scaffold.dart';
+class NoTripsPage extends StatefulWidget {
+  const NoTripsPage({super.key});
+
+  @override
+  State<NoTripsPage> createState() => _NoTripsPageState();
+}
+
+class _NoTripsPageState extends State<NoTripsPage> with ScaffoldLayout {
+  @override
+  Widget build(BuildContext context) => mainScaffold(
+    context,
+    child: Scaffold(
+      body: Center(
+        child: Column(
+          mainAxisAlignment: MainAxisAlignment.center,
+          children: [
+            Text(
+              "No trips yet",
+              style: Theme.of(context).textTheme.headlineMedium,
+            ),
+            Text(
+              "You can start a new trip by clicking the button below",
+              style: Theme.of(context).textTheme.bodyMedium,
+            ),
+          ],
+        ),
+      ),
+      floatingActionButton: FloatingActionButton.extended(
+        onPressed: () {
+          Navigator.of(context).push(
+            MaterialPageRoute(
+              builder: (context) => const NewTripPage()
+            )
+          );
+        },
+        label: const Row(
+          children: [
+            Text("Start planning!"),
+            Padding(padding: EdgeInsets.only(right: 8.0)),
+            Icon(Icons.map_outlined)
+          ],
+        )
+      )
+    )
+  );
+}

frontend/lib/pages/onboarding.dart

@@ -4,6 +4,7 @@ import 'package:anyway/constants.dart';
 import 'package:anyway/modules/onbarding_agreement_card.dart';
 import 'package:anyway/modules/onboarding_card.dart';
 import 'package:anyway/pages/new_trip_location.dart';
+import 'package:anyway/structs/agreement.dart';
 import 'package:flutter/material.dart';
 import 'package:shared_preferences/shared_preferences.dart';
 
@@ -121,11 +122,7 @@ class _OnboardingPageState extends State<OnboardingPage> {
         );
       } else {
         // only allow the user to proceed if they have agreed to the terms and conditions
-        Future<bool> hasAgreed = SharedPreferences.getInstance().then(
-          (SharedPreferences prefs) {
-            return prefs.getBool('TC_agree') ?? false;
-          }
-        );
+        Future<bool> hasAgreed = getAgreement().then((agreement) => agreement.agreed);
 
         return FutureBuilder(
           future: hasAgreed,
@@ -157,8 +154,7 @@ class _OnboardingPageState extends State<OnboardingPage> {
   );
 
   void onAgreementChanged(bool value) async {
-    SharedPreferences prefs = await SharedPreferences.getInstance();
-    await prefs.setBool('TC_agree', value);
+    saveAgreement(value);
     // Update the state of the OnboardingPage
     setState(() {});
   }