Migrate docs website

[jacomyal]

Today, there is only docs.gephi.org, and in the new version, there will be:

• docs.gephi.org (homepage)
• docs.gephi.org/desktop (Gephi
• docs.gephi.org/lite (Gephi Lite)

[sim51]

Technically, it's a rebase of the branch gephi-week-2025-multiple in the master one.
Github actions do the rest.