If no argument is provided, check whether design/assets/asset-manifest.md exists:
- If it exists: read it, find the first context (system/level/character) with any asset at status "Needed" but no spec file written yet, and use
AskUserQuestion: - Prompt: "The next unspecced context is [target]. Generate asset specs for it?"
- Options:
[A] Yes — spec [target]/[B] Pick a different target/[C] Stop here - If no manifest: fail with:
> "Usage: /asset-spec system:<name> — e.g.,
[Description truncada. Veja o README completo no GitHub.]