Draft stories get an annotation review loop, and the story checks catch broken charts

Draft data stories are now published to a private-link Flowershow site with annotations on, so a reviewer can select any passage and leave a note, and an agent pulls the notes with fl annotations pull, revises the story and republishes; drafts stay off this site until approved. The story checks gained S7, which fails any chart SVG containing NaN, undefined or leaked function source, and the story skill now asks writers to state the difference or ratio rather than leave two numbers for the reader to compare.