EXAMPLES:
    # List all sections with block numbers
    iwe extract notes/project --list

    # Extract section by title
    iwe extract notes/project --section "Architecture"

    # Extract section by block number (unambiguous)
    iwe extract notes/project --block 2

    # Preview changes without writing
    iwe extract notes/project --section "Notes" --dry-run

    # Use a specific action from config
    iwe extract notes/project --section "Design" --action "my-extract"

    # Output affected document keys for scripting
    iwe extract notes/project --section "Notes" -f keys

OUTPUT:

    -f markdown (default): progress messages showing extract action.
    -f keys: one affected document key per line. Matches `iwe find -f keys`
        in shape.
