Linear guide

[kofigumbs]

https://typebeat.xyz used to have a more structured tutorial that would guide the user through the various modes in a specific order: https://github.com/kofigumbs/typebeat/tree/8228c61811ab8e1de65c31f51729a3f97c8f31c0

I tested this out with a few people, and noticed some issues:

• It's impractical to cover every mode sequentially. Even the 20 pages I finished had a bit of jumping between SONG and AUDITION mode. This matches how I use Typebeat in practice, but it seemed repetitive in a learning context.
• When you got off-track, it was hard to know and correct. The guide needs to be smart enough to detect if the user is doing their own thing and let them reset to a known state if they want to return. The goal should always be for users to feel comfortable exploring, not for them to get through the guide content.
• It was unclear what the guide was building toward. I think the next version should include an audio clip and say something like "we're going to build this song track-by-track" (idea from @7hoenix).

I replaced the linear guide with the more open-ended help text for now, but it would be fun to explore adding more structure in the future.