DrawingCardDoc + parseDrawingCardDoc read the `clide draw` JSON: card
label/description, primitive svg/svgPath, or a template name plus its
fields (for a handler to lower to SVG). Tolerant — a non-object payload
is null, blank strings are absent, never throws. Flutter-free, covered by
dart test (10 cases). First slice of the drawing-card core (D-103); not
yet wired.
Co-Authored-By: Claude Opus 4.8 (1M context) <noreply@anthropic.com>