Arrowheads, width-profile outlines and dashed line outlines now come from
vectorcraft_effects::stroke (stroke_pieces, line_outline, width_outline), used by
the canvas and PDF export alike; the renderer caches profile outlines too. Width
profiles are a doc-level catalogue (WidthProfile::PRESETS, preset, preset_id,
id_of) shared by stroke.set and the Stroke panel; stroke.set rejects unknown
profile ids and its params doc lists the arrowhead names.
Co-Authored-By: Claude Opus 5.5 <noreply@anthropic.com>