Add intermediate page while loading app

People open apps but do not know it comes from LNFly and what LNFly is.

End users visit /apps/id/view instead of /api/apps/id/view (update all links).

After a 5 seconds the page should then be fully replaced with the content from /api/apps/id/view without doing a redirect. The content should be fetched from /api/apps/id/view using react dangerously set HTML.

What should be on the intermediate page:
- "App created with LNFly" with a link to the home page
- Brief subtitle of what LNFly is
- Apps on LNFly are vibe coded with AI. Use at your own risk.
- A countdown timer + a button to instantly view the app

Make sure it is mobile friendly.

Start by tracing the /apps/id/view entry point and the existing /api/apps/id/view links and response handling. Implement the mobile-friendly intermediate page with LNFly messaging, a five-second countdown, an instant-view button, and content fetched into the page with React dangerouslySetInnerHTML; done means the app content replaces the page without a redirect.

Written by the indexing model from the issue text.