For agents, on top of README.md, which they read first.

Notes for agents

• Only art_*.rs know what a mascot looks like. Scenes, decorations and motion are whiskers-art's. A new mascot is a variant of Mascot and a figure(mood) that matches every Mood without a wildcard.
• css::stylesheet is built from the motions the scenes use; do not list motions by hand.
• Do not hand-edit generated markup; edit the scene.
• Do not add a dependency beyond the two workspace crates. This crate compiles to wasm and to the preview tool.