fix: deduplicate overdue logic into TodoItem.isOverdue computed property

MindDump/Models/TodoItem.swift

@@ -13,6 +13,13 @@ class TodoItem: Identifiable {
     var modifiedAt: Date?
     var list: TodoList?
 
+    var isOverdue: Bool {
+        guard !isCompleted, let deadline else { return false }
+        return deadline < Calendar.current.startOfDay(
+            for: Calendar.current.date(byAdding: .day, value: 1, to: Date())!
+        )
+    }
+
     init(
         id: UUID = UUID(),
         title: String,

MindDump/ViewModels/ListStore.swift

@@ -194,8 +194,7 @@ class ListStore {
     }
 
     private func isDue(_ item: TodoItem) -> Bool {
-        let startOfTomorrow = Calendar.current.startOfDay(for: Calendar.current.date(byAdding: .day, value: 1, to: Date())!)
-        return item.deadline != nil && item.deadline! < startOfTomorrow
+        item.isOverdue
     }
 
     private func save() {

MindDump/Views/TodoRowView.swift

@@ -6,13 +6,6 @@ struct TodoRowView: View {
     var subtitle: String?
     var onTap: (() -> Void)?
 
-    private var isOverdue: Bool {
-        !item.isCompleted && item.deadline != nil
-            && item.deadline! < Calendar.current.startOfDay(
-                for: Calendar.current.date(byAdding: .day, value: 1, to: Date())!
-            )
-    }
-
     var body: some View {
         HStack {
             Button(action: onToggle) {
@@ -52,13 +45,13 @@ struct TodoRowView: View {
                     .foregroundStyle(priority.color)
             }
 
-            if isOverdue {
+            if item.isOverdue {
                 Image(systemName: "exclamationmark.circle.fill")
                     .font(.system(size: 14))
                     .foregroundStyle(.red)
             }
         }
-        .listRowBackground(isOverdue ? Color.red.opacity(0.08) : nil)
+        .listRowBackground(item.isOverdue ? Color.red.opacity(0.08) : nil)
     }
 
     private func noteSnippet(_ text: String) -> String {