Diagrams, artifact kinds and the composer

A batch of things that were visibly wrong.

• Inline timelines were unreadable — every event rendered as a narrow strip of text, one word per line. Diagrams also only had about half the colour palette wired up, so a chart asking for its third or fifth colour came back grey.
• Asking for a visual of a document produced a wall of CSS. The model was saving an HTML page as a new version of the existing document, which then rendered as source. Asking for the same subject in a different form now creates a new artifact instead.
• The composer settled down. No more pale box appearing around the text when the pointer crosses it, and no border lighting up the moment the page loads. The model picker sits next to the effort setting as one phrase rather than a name floating a hundred pixels from its own chevron.
• "New chat" from the chats list created a real, empty conversation every time it was clicked. It opens the compose screen now, and a conversation exists once something is said in it.
• Bring-your-own-keys is built from the same parts as the rest of settings, instead of section headings rendering as filled bands across the page.