WIBNI guidance for new users at first startup

Currently Dyalog opens with a mostly blank session. Unfamiliar users are left wondering what to click or do to start using the system. Wouldn't It Be Nice If there was a friendly message that gave users the bare minimum information required to use the Session (enter expressions) and save their work in a modern way (Link).

Relatedly, it is a shame that the File Save / Open menu items deal only with binary workspaces, when we are now recommending source in text files.

Start with qSE's ⎕SE initialization path and trace what runs when Dyalog opens a mostly blank Session. Review how the File Save/Open menu items are handled. Done means first-time users receive basic Session and Link guidance, while file operations reflect the recommended text-source workflow.

Written by the indexing model from the issue text.