Add a "Draw Cut Direction" toggle to the View menu that draws small
arrowheads along cutting paths to indicate the direction of travel.
Arrows are placed on both linear and arc moves, spaced ~60px apart,
and correctly follow CW/CCW arc tangents.
Extract all rendering methods (~660 lines) from PlateView into a new
PlateRenderer class, reducing PlateView from 1640 to 979 lines.
PlateView retains input handling, selection, zoom, and part management.
Co-Authored-By: Claude Opus 4.6 (1M context) <noreply@anthropic.com>