[Rolodex] Update fidelity of Contact list screens (#2588)

This PR:

- Updates the fidelity of the home screen and contact list screens to near full fidelity
- Renames "Contact Lists" to "Contact Groups". We have multiple collections of contacts, so having lists of lists felt confusing
- Adds more functionality to the data models

Comparison of the two screens against native:

| Native | Flutter |
| --- | --- |
| <img width="418" alt="Screenshot 2025-02-19 at 2 59 58 PM" src="https://github.com/user-attachments/assets/1cc53d19-6bb5-4782-82fa-1a62cd75fd51" /> | <img width="397" alt="Screenshot 2025-02-19 at 2 58 54 PM" src="https://github.com/user-attachments/assets/ddab75f2-4aec-4239-a736-690a3185c196" /> |
| <img width="409" alt="Screenshot 2025-02-19 at 2 59 41 PM" src="https://github.com/user-attachments/assets/ee0d81ee-ae60-47ad-b071-266f39ce9b70" /> | <img width="402" alt="Screenshot 2025-02-19 at 2 58 45 PM" src="https://github.com/user-attachments/assets/88bf22f9-d8bd-40d7-a9ca-f2ded439de6c" /> |

Notably the container widget on the first screen is a placeholder, until a Cupertino collapsable widget is made.

rolodex/lib/main.dart

@@ -5,9 +5,9 @@
 import 'package:flutter/cupertino.dart';
 import 'package:provider/provider.dart';
 
-import 'data/contact_list.dart';
+import 'data/contact_group.dart';
 import 'screens/contacts.dart';
-import 'screens/lists.dart';
+import 'screens/contact_groups.dart';
 
 void main() {
   runApp(const RolodexApp());
@@ -19,16 +19,22 @@ class RolodexApp extends StatelessWidget {
   @override
   Widget build(BuildContext context) {
     return ChangeNotifierProvider(
-      create: (context) => ContactListsModel(),
+      create: (context) => ContactGroupsModel(),
       child: CupertinoApp(
         title: 'Rolodex',
+        theme: CupertinoThemeData(
+          barBackgroundColor: CupertinoDynamicColor.withBrightness(
+            color: Color(0xFFF9F9F9),
+            darkColor: Color(0xFF1D1D1D),
+          ),
+        ),
         initialRoute: '/contacts',
         onGenerateInitialRoutes: (initialRoute) {
           return [
             CupertinoPageRoute(
               title: 'Lists',
               builder: (BuildContext context) {
-                return ListsPage();
+                return ContactGroupsPage();
               },
             ),
             CupertinoPageRoute(