19 of 28 showcase previews are 1280x720; spec is 1200x675 and nothing enforces it #214

What

CLAUDE.md specifies preview webps at 1200×675 (heroes at 1280×720). All 51 example previews conform, but 19 of 28 showcase previews are 1280×720:

stone-well, campfire, market-stall, street-lantern, terrain-scatter, fence-kit, watchtower, cart, park-bench, anvil, water-trough, hitching-post, hand-pump, signpost, chopping-block, wall-torch, wooden-ladder, crate-stack, stone-archway

Measured with Pillow against the preview path of every showcase/gallery.json entry.

Why it matters

Low impact today: the site never serves previews. crate-stack and stone-archway embed theirs in their README, but the gallery drops those images since #208. The real problem is that nothing enforces the spec, so it drifts.

Suggested fix

1. Downscale the 19 to 1200×675. Same aspect ratio, so no re-render is needed.
2. Have validate.yml or build_gallery.py assert hero 1280×720 and preview 1200×675 for every gallery entry.

Related: #200. If those heroes are regenerated, regenerate previews from the same render.