fix(canvas): persist strokes, pressure, slider

Strokes vanished on pen-up: StaticInkPainter aliased the same mutable
list so shouldRepaint saw no change. Commit/erase now replace the list.
Finger-drawing toggle wins over palm-rejection; pressure surfaces even
when the pen reports no min/max range; pages recenter after a flip; the
keyboard page-jump (unreliable on Windows) is now a drag slider. Also
register the dynamic_color plugin in generated registrants.

macos/Flutter/GeneratedPluginRegistrant.swift

@@ -6,6 +6,7 @@ import FlutterMacOS
 import Foundation
 
 import device_info_plus
+import dynamic_color
 import file_picker
 import file_selector_macos
 import flutter_onnxruntime
@@ -16,6 +17,7 @@ import url_launcher_macos
 
 func RegisterGeneratedPlugins(registry: FlutterPluginRegistry) {
   DeviceInfoPlusMacosPlugin.register(with: registry.registrar(forPlugin: "DeviceInfoPlusMacosPlugin"))
+  DynamicColorPlugin.register(with: registry.registrar(forPlugin: "DynamicColorPlugin"))
   FilePickerPlugin.register(with: registry.registrar(forPlugin: "FilePickerPlugin"))
   FileSelectorPlugin.register(with: registry.registrar(forPlugin: "FileSelectorPlugin"))
   FlutterOnnxruntimePlugin.register(with: registry.registrar(forPlugin: "FlutterOnnxruntimePlugin"))