Add notebook draw mode to study and reader pages

Draw mode in the study page replaces all note panels with a full ruled
notebook canvas (no cross-refs, observations, or text boxes) so the user
has a clean writing surface. Ink strokes are saved per chunk and exported
as SVG in the HTML export.

The reader page gets a Draw toggle button that reveals the same notebook
canvas below the verse list, with strokes persisted per book+chapter in
localStorage via readerInkByPage.

Co-Authored-By: Claude Sonnet 4.6 <noreply@anthropic.com>

src/utils/inkRender.js

@@ -1,6 +1,6 @@
 import { getStroke } from 'perfect-freehand';
 
-function pathFromStroke(points) {
+export function pathFromStroke(points) {
   if (!points.length) return '';
   const d = [`M ${points[0][0].toFixed(2)} ${points[0][1].toFixed(2)}`];
   for (let i = 1; i < points.length - 1; i++) {