refactor: set sortOrder when creating new Project

Todos/Model/Project.swift

@@ -21,8 +21,9 @@ final class Project: Codable, Ordered, Aggregate {
   @Relationship(deleteRule: .cascade, inverse: \Task.project)
   var tasks: [Task] = []
 
-  init(timestamp: Date) {
+  init(timestamp: Date, sortOrder: Int = 0) {
     self.timestamp = timestamp
+    self.sortOrder = sortOrder
   }
 
   func move(fromOffsets: IndexSet, toOffset: Int) {

Todos/View/ContentView.swift

@@ -51,7 +51,7 @@ struct ContentView: View {
 
   private func addItem() {
     withAnimation {
-      let newItem = Project(timestamp: Date())
+      let newItem = Project(timestamp: Date(), sortOrder: items.count)
       modelContext.insert(newItem)
     }
   }

Todos/View/Menu/NewProjectMenu.swift

@@ -19,7 +19,7 @@ struct NewProjectMenu: View {
 
   private func addItem() {
     withAnimation {
-      let newItem = Project(timestamp: Date())
+      let newItem = Project(sortOrder: items.count)
       modelContext.insert(newItem)
     }
   }