[Task]: Add welcome screen for onboarding

[paul-boegelsack]

Task description

Add welcome screen as router component to the mobile package and adjust the presentation.

Requirements

• [ ] Router component added to the mobile project
• [ ] Presentation adjusted for mobile

Creation checklist

• [ ] I have assigned this task to the correct people
• [X] I have added the most appropriate labels
• [X] I have linked the correct milestone and/or project