Keep draw mode active when navigating chapters in reader

Previously draw mode was closed whenever the book or chapter changed.
Now it stays open so the user can flip between chapters while drawing;
each chapter has its own canvas (ink is keyed per bookAbbrev_chapter).

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

src/pages/ReaderPage.jsx

@@ -51,7 +51,6 @@ export default function ReaderPage() {
   const [readerDrawMode, setReaderDrawMode] = useState(false);
   const readerPageInkStrokes = readerInkByPage?.[`${readerBookAbbrev}_${readerChapter}`] ?? [];
 
-  useEffect(() => { setReaderDrawMode(false); }, [readerBookAbbrev, readerChapter]);
   const bookmarkEntries = Object.entries(readerBookmarks).map(([key, color]) => {
     const [bAbbrev, chapterStr, verseStr] = key.split('-');
     const bookIndex = bookOptions.findIndex((b) => b.abbrev === bAbbrev);