update how linebreaks are saved so they render properly in perseus

[marcellamaki]

Summary

Addresses the second part of: #5894

(This was not a regression, thus we will put in our first patch release)

References

Fixes #5894

Reviewer guidance

1. Confirm line breaks save and display properly on Studio -- in initial create and on save/edit
2. export to kolibri
3. confirm line breaks appear properly in ANSWER rendering

AI usage

I used claude to both identify the cause of the issue and implement the solution here