refactor: add chevrons to onboarding screens

[ItsANameToo]

Summary

https://app.clickup.com/t/86du2czk8

TODO:

• properly handle interval clearing (or refactor completely)
• ensure progressbar moves with the slides instead of being its own thing

Checklist

• I checked that both pnpm dev and pnpm dev:bare work as intended
• I checked the basic extension interactions and made sure wallet selection works
• I checked my UI changes against the design and there are no notable differences, including responsiveness
• I checked my (code) changes for obvious issues, debug statements and commented code
• I opened a corresponding card on Clickup for any remaining TODOs in my code
• I added a short description on how to test this PR (if necessary)
• Ready to be merged