Docs: Increase user of screenshots within our documentation

### Description

Our docs are very text heavy, and include a lot of instructions around using the FlowFuse platform, but miss any screenshots. This can be difficult to maintain long term, but the text-heavy structure and content gives the impression of these tasks being difficult/technical to do. Showing off our UI can lighten the expectation of the user, and be more encouraging for them to use particular features.

Start by reviewing the FlowFuse documentation and its text-heavy instructions for using the platform. The issue provides no specific files, pages, or tests; the work is done when an agreed set of relevant documentation tasks includes useful UI screenshots and the surrounding guidance remains clear.

Written by the indexing model from the issue text.