minor fixes + use modstorage instead file storage

[nonfreegithub]

No description provided.

[SmallJoker]

Why are the comments in Spanish?
What does that contentReference mean?
Might an LLM be involved during this process?

[nonfreegithub]

sorry, comments removed

[SmallJoker]

I pushed the first three commits to master as they were important bugfixes. As for the mod storage part - it honestly looks .. strange.

1. The data save code and the new part of the migration are currently duplicates.
2. The mod would need a proper check against Minetest >= 5.7 upon startup to show a helpful error to the user.
3. mod.conf needs a version entry for >= 5.7.
4. Some of the new comments describe what the line below does. That's not helpful. They should describe WHY it's being done like that (if necessary at all).