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/pdf/src/lib.rs

@@ -1,7 +1,9 @@
 //! VectorCraft PDF export and import.
 //!
 //! - [`export`] writes one PDF page per artboard with `krilla`: vector paths (fills, strokes with
-//!   caps/joins/miter/dashes, non-zero/even-odd), opacity and blend modes (transparency groups),
+//!   caps/joins/miter/dashes, inside/outside alignment as clips, non-zero/even-odd; arrowheads,
+//!   width profiles, fitted or dotted dashes as the canvas's filled outlines and brushed strokes
+//!   as their brush art), opacity and blend modes (transparency groups),
 //!   clip groups, linear/radial gradients (shadings), embedded images and text as outlined glyph
 //!   paths. Hidden objects, guides and template layers are skipped.
 //! - [`import`] reads PDF (and PDF-compatible `.ai`) pages with `hayro-interpret` into a
@@ -107,3 +109,5 @@ pub enum PdfError {
 mod tests;
 #[cfg(test)]
 mod tests_stroke;
+#[cfg(test)]
+mod tests_strokeout;