migrate change-appearance page to app router

[therungg]

GitHub thinks I renamed and changed a bunch, which makes review hard, but here's a summary:

• Removed pages/change-appearance.tsx
• Added a Server Component app/change-appearance/page.tsx which fetches some data
• Added two Client Components as leaves of the Server Component
• Added an api route /api/change-appearance, that does the same as /api (for logging in), but redirects back to the original page
• Moved the logic to check a patron's status to a seperate action