chore: update macOS plugin registrant for shared_preferences

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

macos/Flutter/GeneratedPluginRegistrant.swift

@@ -5,6 +5,8 @@
 import FlutterMacOS
 import Foundation
 
+import shared_preferences_foundation
 
 func RegisterGeneratedPlugins(registry: FlutterPluginRegistry) {
+  SharedPreferencesPlugin.register(with: registry.registrar(forPlugin: "SharedPreferencesPlugin"))
 }