Use drawing controller

lib/features/sheet_viewer/sheet_viewer_page.dart

@@ -1,6 +1,8 @@
 import 'package:flutter/foundation.dart';
 import 'package:flutter/material.dart';
 import 'package:flutter/services.dart';
+import 'package:flutter_drawing_board/flutter_drawing_board.dart';
+import 'package:flutter_drawing_board/paint_contents.dart';
 import 'package:flutter_fullscreen/flutter_fullscreen.dart';
 import 'package:logging/logging.dart';
 import 'package:pdfrx/pdfrx.dart';
@@ -41,10 +43,20 @@ class _SheetViewerPageState extends State<SheetViewerPage>
   int _currentPage = 1;
   int _totalPages = 1;
   bool _isPaintMode = false;
+  late DrawingController _drawingController;
 
   @override
   void initState() {
     super.initState();
+    // Initialize drawing controller with default configuration
+    _drawingController = DrawingController(
+      config: DrawConfig(
+        contentType: SimpleLine,
+        strokeWidth: 4.0,
+        color: Colors.black,
+      ),
+      maxHistorySteps: 100, // Limit undo/redo history (default: 100)
+    );
     FullScreen.addListener(this);
     FullScreen.setFullScreen(widget.config.fullscreen);
     _documentLoaded = _loadPdf();
@@ -52,6 +64,7 @@ class _SheetViewerPageState extends State<SheetViewerPage>
 
   @override
   void dispose() {
+    _drawingController.dispose();
     FullScreen.removeListener(this);
     _document?.dispose();
     super.dispose();
@@ -225,7 +238,10 @@ class _SheetViewerPageState extends State<SheetViewerPage>
         // Show paint mode layer when active
         Visibility(
           visible: _isPaintMode,
-          child: PaintModeLayer(pageDisplay: pageDisplay),
+          child: PaintModeLayer(
+            pageDisplay: pageDisplay,
+            drawingController: _drawingController,
+          ),
         ),
       ],
     );

lib/features/sheet_viewer/widgets/paint_mode_layer.dart

@@ -6,13 +6,15 @@ import 'pdf_page_display.dart';
 /// Drawing overlay for annotating PDF pages.
 ///
 /// Uses flutter_drawing_board to provide a paint canvas over the PDF.
-/// Only available in single-page mode.
+/// Only working in single-page mode.
 class PaintModeLayer extends StatelessWidget {
   final PdfPageDisplay pageDisplay;
+  final DrawingController drawingController;
 
   const PaintModeLayer({
     super.key,
     required this.pageDisplay,
+    required this.drawingController,
   });
 
   @override
@@ -24,6 +26,7 @@ class PaintModeLayer extends StatelessWidget {
           final (pageSize, _) = pageDisplay.calculateScaledPageSizes(maxSize);
 
           return DrawingBoard(
+            controller: drawingController,
             background: SizedBox(
               width: pageSize.width,
               height: pageSize.height,