feat(site): rebuild the promo with one headline per scene and the current outputs

CHANGELOG.md

@@ -41,6 +41,7 @@ Until the first release, changes are recorded under [Unreleased].
 
 ### Changed
 
+- The promo video (`site/promo/`), rebuilt for what the skill makes now: the deck in the outputs and the drawing of how it works, and Fig. 2 named in the margin as the post now draws it. Each scene has one headline in the same place and short labels at most; the post's own text is greeked, as on the home page's canvas. It builds again after `dossier` left `site/iso.mjs`.
 - `anatomy`: the flat and screenshot views put each key's text in the margin, joined to its part by a hairline (a bracket for a key with `"span": true`, a dot otherwise), instead of numbered discs and a legend. Below about 560px they fall back to small numbers and the legend; `"notes": "keys"` keeps the old hotspots, and iso always uses them. The flat view takes the iso view's tones with an offset shadow, and its list rows are drawn as raised slabs. The weekly-digests card is drawn flat instead of iso, and the committed weekly-digests and walkthrough-videos posts and the README's hero and example images are re-rendered with margin notes. The examples page and `docs/components.md` show the new hero in place of the iso "apart" picture (`digest-apart.webp` is removed), and the link previews are rebuilt. `lint.mjs` counts margin notes as hotspots, and `inline-assets.mjs` and the gallery handle an SVG `<image href>`.
 
 - Length guidance sizes a post by the scope of the change, with bands measured against published Cloudflare and Astro posts (`references/story.md`). The deep dive gets a soft ceiling of about 3,000 words: `lint.mjs` warns past it and the author can let it stand.