First layer of the scene template center: the data model behind "pick a
scene, get a finished document". Templates differ from Prompt Center
entries in what they produce — a document to edit, not text for the
model — so each entry embeds its `.op` and the catalogue refuses to load
when one is missing. A prompt without a preview still works; a template
without a document is a card that does nothing when clicked, which is
worse than no card at all.
The three step-0 documents move from `templates/` into the crate's
assets: they are shipped content now, and one authoritative copy beats a
source and an embedded duplicate that drift. `templates/step0` keeps the
generators and their full-resolution renders — the workshop, not the
shelf — and `previews.sh` follows the documents to their new home.
Card previews are baked to the prompt-center convention (640x400 JPEG,
13-15 KB) by a new generator. The panel paints every card through one
fixed rect with `ImageDrawMode::Fill`, so a 2160x2880 page render or a
5880x1440 overview would be cropped to an unreadable strip; the baker
fits the whole design inside the card and pads with the document's own
backdrop, sampled from the render's corners.
The TOML value parsers move to a shared `catalog_toml` rather than being
copied for the second catalogue. Each catalogue keeps its own error type
so the messages still name the right asset file; only the parsing is
shared. Prompt Center behaviour is unchanged (its 14 tests still pass).
Claude-Session: https://claude.ai/code/session_01FqKQqNj8exYwopGDpYUU7x
20cfbddd4b