Gallery alt text describes the API, not the picture

[TMHSDigital]

What

Gallery image alt text describes the API an entry teaches, not what the picture shows.

• Gallery cards: card_alt() in scripts/build_gallery.py builds "{name} — {first sentence of teaches}", capped at 160 characters. 29 of 79 alts are cut with "…". As of fix(site): finish the Pages review follow-ups #209, the card's image link is aria-hidden, so card alts no longer reach screen readers at all.
• Detail-page hero and zoom image: "{name} render" and "{name} render, full size".
• Landing-page cards: "{name} render" (scripts/site/template.html.j2).

"swatch-grid render" tells a screen-reader user nothing about the image. The READMEs already contain good visual descriptions, e.g. showcase/crate-stack/README.md's image alt: "Three shipping crates stacked, each yawed and offset differently".

Proposal

• Add an optional alt field to each examples/gallery.json / showcase/gallery.json entry: one sentence describing the picture.
• Use it for the detail-page hero, the zoom image and the landing cards, falling back to today's text.
• Once backfilled, have build_gallery.py require it for new entries, the way it already guards alts against dotted-path truncation.

79 one-line descriptions: content work, not code.