feat: add sound and vibration feedback for registration actions

Integrate audioplayers, vibration, and file_picker packages to provide
audio/haptic feedback on registration success/failure. Add sound
settings UI in SettingsPage for customizing notification sounds.

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

windows/flutter/generated_plugin_registrant.cc

@@ -6,6 +6,9 @@
 
 #include "generated_plugin_registrant.h"
 
+#include <audioplayers_windows/audioplayers_windows_plugin.h>
 
 void RegisterPlugins(flutter::PluginRegistry* registry) {
+  AudioplayersWindowsPluginRegisterWithRegistrar(
+      registry->GetRegistrarForPlugin("AudioplayersWindowsPlugin"));
 }

windows/flutter/generated_plugins.cmake

@@ -3,9 +3,11 @@
 #
 
 list(APPEND FLUTTER_PLUGIN_LIST
+  audioplayers_windows
 )
 
 list(APPEND FLUTTER_FFI_PLUGIN_LIST
+  jni
 )
 
 set(PLUGIN_BUNDLED_LIBRARIES)