Add Draw mode for Apple Pencil annotation on scripture panel

Adds a third layout option alongside Stacked and Split. In Draw mode a
canvas overlay covers the scripture panel; the Pointer Events API routes
Apple Pencil input to perfect-freehand strokes while letting finger
touches fall through for normal scrolling. A floating toolbar provides
pen, highlighter, and eraser tools, six color swatches, S/M/L sizes,
undo, clear, and a Done button to return to Stacked view.

Strokes are stored as inkStrokes[] on each chunk and rendered as a
read-only transparent canvas overlay (InkLayer) in Stacked/Split modes.
migrateChunk is updated so all existing chunks get inkStrokes: [] on
first load.

Also adds a simple in-memory rate limiter on auth endpoints (10 attempts
per 15 min per IP).

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

src/App.jsx

@@ -168,6 +168,7 @@ export function migrateChunk(chunk) {
       episodeTitle: chunk.episodeTitle ?? '',
       finalScript: chunk.finalScript ?? '',
       tags: chunk.tags ?? [],
+      inkStrokes: chunk.inkStrokes ?? [],
     }; // already new format
   }
   return {
@@ -177,6 +178,7 @@ export function migrateChunk(chunk) {
     application: '',
     crossReferences: [],
     tags: [],
+    inkStrokes: [],
     spilloverEndVerse: null,
     generalNotes: '',
     episodeNumber: '',
@@ -1283,7 +1285,10 @@ const App = () => {
   }, []);
   const [studyLayout, setStudyLayout] = useState(
     () => localStorage.getItem('studyLayout') || 'stacked',
-  ); // 'stacked' | 'split'
+  ); // 'stacked' | 'split' | 'annotate'
+  const [drawTool, setDrawTool] = useState('pen');
+  const [drawColor, setDrawColor] = useState('#0f172a');
+  const [drawSize, setDrawSize] = useState(0.012);
   const [activeStudyTab, setActiveStudyTab] = useState(
     () => localStorage.getItem('activeStudyTab') || 'notes',
   );
@@ -3751,6 +3756,9 @@ const deleteProject = (id) => {
     selectedChunkVerses,
     selectedChunkGlobalIndex,
     studyLayout, setStudyLayout,
+    drawTool, setDrawTool,
+    drawColor, setDrawColor,
+    drawSize, setDrawSize,
     activeStudyTab, setActiveStudyTab,
     mobileStudyTab, setMobileStudyTab,
     collapsedSections, setCollapsedSections,