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>

package-lock.json

@@ -17,6 +17,7 @@
         "express-session": "^1.19.0",
         "mammoth": "^1.12.0",
         "otplib": "^12.0.1",
+        "perfect-freehand": "^1.2.3",
         "qrcode": "^1.5.4",
         "react": "^19.0.0",
         "react-dom": "^19.0.0"
@@ -4970,6 +4971,12 @@
       "dev": true,
       "license": "MIT"
     },
+    "node_modules/perfect-freehand": {
+      "version": "1.2.3",
+      "resolved": "https://registry.npmjs.org/perfect-freehand/-/perfect-freehand-1.2.3.tgz",
+      "integrity": "sha512-bHZSfqDHGNlPpgH2yxXgPHlQSPpEbo+qg7li0M78J9vNAi2yjwLeA4x79BEQhX44lEWpCLSFCeRZwpw0niiXPA==",
+      "license": "MIT"
+    },
     "node_modules/picocolors": {
       "version": "1.1.1",
       "resolved": "https://registry.npmjs.org/picocolors/-/picocolors-1.1.1.tgz",