feat: new onboarding screens (#4)

Changelog:
- Add a custom splash screen
- Redesign the onboarding screen
- Improve UX for the new and import identity screens

Reviewed-on: #4

composeApp/src/androidMain/AndroidManifest.xml

@@ -20,7 +20,8 @@
         android:theme="@android:style/Theme.Material.Light.NoActionBar">
         <activity
             android:name=".MainActivity"
-            android:exported="true">
+            android:exported="true"
+            android:theme="@style/Theme.App.Starting">
             <intent-filter>
                 <action android:name="android.intent.action.MAIN" />
                 <category android:name="android.intent.category.LAUNCHER" />