Suggestion: Moving content of `slides` folders to tutorials

Hi,

For a while, I found the `slides` folders in topics confusing:
- The content is a bit lonely on its side
- It can not be listed as prerequisite or follow-up in tutorials (in different topics)

What we can do:
- moving content of the `slides` folders to tutorials
- use the subtopics and define one as "introduction" that always goes to top

What do you think about this?

Start by inventorying the existing `slides` folders and the tutorial and subtopic structure across the training material. Review how prerequisites, follow-ups, and an introductory subtopic are currently represented; done means the proposed organization is defined and the affected content has been consistently moved without losing those relationships.

Written by the indexing model from the issue text.