feat: add UserDefaults for Category settings

Todos/TodosApp.swift

@@ -12,6 +12,7 @@ struct UserDefaultsKeys {
   private static let root = "leumasjaffe.Todos"
   static let UrlHints = root + ".URLHints"
   static let WeekStart = root + ".WeekStart"
+  static let Category = root + ".Category"
 }
 
 @main

Todos/View/Settings/CategoryGroupView.swift

@@ -8,7 +8,7 @@
 import SwiftUI
 
 struct CategoryGroupView: View {
-  @State var allGroups = [Category]()
+  @AppStorage(UserDefaultsKeys.Category) var allGroups = CodableArray<Category>()
   @State var active = Category()
   
   var body: some View {