📝 Documentation: Link demos to playground

[JoshuaKGoldberg]

Documentation Checklist

• I have pulled the latest main branch of the repository.
• I have searched for related issues and found none that matched my issue.

Overview

Right now, the site has two ways to see a bunch of different emoji-blast triggers:

• #5124 added https://www.emojiblast.dev/playground
• https://www.emojiblast.dev/demos already existed with a bunch of custom triggers

It'd be cool if the demos also included a link to the playground. That way you could tweak them yourself.

Additional Info

Should we eventually unify the two in some way? 🤷 a longer thought process for later.

Marking as initially blocked on #1529 for URL state syncing. Which is itself blocked on #1528, investigating security.

🎆