Scaffold a vignette catalog

A catalog starts as a manifest and one useful notebook, not a package or pipeline. Ask for the catalog name, target path, and data surface (rest, duckdb, pooch, or files) only when they cannot be inferred.

Workflow

1. Inspect the target. For a new catalog, require an absent or empty directory. For an existing repository, preserve its files and use --adopt.

2. Generate the minimum structure:

   <skill-dir>/scripts/scaffold.py <target> --name <name> --surface <surface>
   # Existing repository:
   <skill-dir>/scripts/scaffold.py <target> --name <name> --surface <surface> --adopt