Also:

* Do not crash when session has no history
* Tv-frame style for embeds

Allow img tag from media libraries
(avoid img hallucinations)

decrease hallucinated img tags

Also display flash messages if needed

Used to make the post send empty field.
Tweak: disable on setTimeout

`prompt.txt` template also contains (via jinja)

* chat.schema.json
* chat-example.json
* in the future, there will be patient-specific variants

`/img` is an image generator (handy)

Updates `static/slides.json` (copies backup `archive/`)