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.

linux/flutter/generated_plugin_registrant.cc

@@ -6,11 +6,15 @@
 
 #include "generated_plugin_registrant.h"
 
+#include <dynamic_color/dynamic_color_plugin.h>
 #include <file_selector_linux/file_selector_plugin.h>
 #include <flutter_onnxruntime/flutter_onnxruntime_plugin.h>
 #include <url_launcher_linux/url_launcher_plugin.h>
 
 void fl_register_plugins(FlPluginRegistry* registry) {
+  g_autoptr(FlPluginRegistrar) dynamic_color_registrar =
+      fl_plugin_registry_get_registrar_for_plugin(registry, "DynamicColorPlugin");
+  dynamic_color_plugin_register_with_registrar(dynamic_color_registrar);
   g_autoptr(FlPluginRegistrar) file_selector_linux_registrar =
       fl_plugin_registry_get_registrar_for_plugin(registry, "FileSelectorPlugin");
   file_selector_plugin_register_with_registrar(file_selector_linux_registrar);

linux/flutter/generated_plugins.cmake

@@ -3,6 +3,7 @@
 #
 
 list(APPEND FLUTTER_PLUGIN_LIST
+  dynamic_color
   file_selector_linux
   flutter_onnxruntime
   url_launcher_linux