Deprecate long instructor note by redesigning Activity 1.2.12

[StevenClontz]

Paragraphs: Instructor Note

This can be wontfix but 99% of the time I suspect that a long instructor note is kludge to make up for an inadequately designed activity. I suspect there was some discussion to get where we are today, but this might be a good issue for someone to look here with fresh eyes and come up with something more intrinsically motivated.

[siwelwerd]

I like this instructor note and think our books generally would benefit from more of these. This might (or a different instructor. note at the beginning of the section) be a good place to link to https://doi.org/10.1080/10511970.2025.2518531 as well.

I do think changing "the following activity" to xref the actual activity would be good though, as I had a half thought that if our instructor notes all were written to make sense as independent pieces they could all potentially be pulled out and collected into a single document or appendix relatively easily.

I do wonder if longer instructor notes should be knowled/collapsed by default though.