M3.36: SVG and PDF export draw arrowheads, width profiles, brushes and aligned strokes as the canvas does

Both writers now ask the shared stroke geometry how to write each stroke
(effects::stroke::for_writer): a plain stroke where that is exact, else the
canvas's filled outlines (arrowheads, width profiles, dashes fitted to corners,
dots with round or projecting caps), grouped under the stroke opacity when the
line and its heads overlap. Brushed strokes are written as their brush art.
Inside/outside alignment only applies to closed paths, so open paths export as
centred strokes. The PDF outside-stroke clip frame and the SVG outside mask now
cover the whole stroke reach (miter spikes, projecting caps). SVG stroke
gradients use the same paint box as the canvas. The svg crate docs no longer
claim arrowheads, profiles, brushes and effects are dropped.

Co-Authored-By: Claude Opus 5.5 <noreply@anthropic.com>

crates/effects/src/stroke.rs

@@ -8,7 +8,7 @@
 //! - [`width_outline`]: variable-width (profile) strokes;
 //! - [`line_outline`]: the line part of a stroke as one filled outline (profile, dashes, dots,
 //!   caps and joins);
-//! - [`outline_region`]: a stroke as one clean filled path (Outline Stroke).
+//! - [`for_writer`] and [`outline_region`]: strokes for the SVG/PDF writers and Outline Stroke.
 
 mod arrow;
 mod dash;
@@ -22,7 +22,7 @@ use vectorcraft_doc::{LineCap, LineJoin, StrokeAlign, StrokeLayer};
 
 pub use arrow::Arrow;
 pub use dash::{Dashed, Dot, dash, dot_outline};
-pub use outline::{OUTLINE_TOL, outline_region};
+pub use outline::{OUTLINE_TOL, Written, WrittenShape, for_writer, is_plain, outline_region};
 pub use width::width_outline;
 
 /// Arc-length accuracy for dashing and trimming (document points).