Renders movable {rootStr,offsets} and open {frets,onlyRoot} KB shapes; computes movable
base fret from chord rootPc in standard tuning (E-shape A7 -> fret 5); root in accent
purple; thumb/full sizes; graceful '-' fallback for unplaceable shapes. Critic PASS.
Co-Authored-By: Claude Fable 5 <noreply@anthropic.com>
vadimwit