Feature: ToDo Lists, Display Names and Sync logic bugfix

- Created ToDo list functionality (CRUD) with household support.

- Linked ToDo lists to packing lists and displayed them on the packing list overview page.

- Added 'display_name' to users table, allowing separation of login name and display name.

- Fixed the irregular '+' click bug in Phase 1 by completely decoupling the local UI state updates from the backend sync latency, relying purely on DOM syncing.

migrate.php

@@ -0,0 +1,39 @@
+<?php
+require_once 'src/db_connect.php';
+
+$queries = [
+    "ALTER TABLE users ADD COLUMN display_name VARCHAR(255) DEFAULT NULL",
+    
+    "CREATE TABLE IF NOT EXISTS todo_lists (
+        id INT AUTO_INCREMENT PRIMARY KEY,
+        user_id INT NOT NULL,
+        household_id INT DEFAULT NULL,
+        name VARCHAR(255) NOT NULL,
+        created_at TIMESTAMP DEFAULT CURRENT_TIMESTAMP,
+        FOREIGN KEY (user_id) REFERENCES users(id) ON DELETE CASCADE,
+        FOREIGN KEY (household_id) REFERENCES households(id) ON DELETE CASCADE
+    )",
+    
+    "CREATE TABLE IF NOT EXISTS todo_items (
+        id INT AUTO_INCREMENT PRIMARY KEY,
+        todo_list_id INT NOT NULL,
+        title VARCHAR(255) NOT NULL,
+        is_completed TINYINT(1) DEFAULT 0,
+        order_index INT DEFAULT 0,
+        FOREIGN KEY (todo_list_id) REFERENCES todo_lists(id) ON DELETE CASCADE
+    )",
+    
+    "ALTER TABLE packing_lists ADD COLUMN todo_list_id INT DEFAULT NULL",
+    "ALTER TABLE packing_lists ADD CONSTRAINT fk_packing_list_todo FOREIGN KEY (todo_list_id) REFERENCES todo_lists(id) ON DELETE SET NULL"
+];
+
+foreach ($queries as $q) {
+    echo "Running: $q\n";
+    if (!$conn->query($q)) {
+        echo "Error: " . $conn->error . "\n";
+    } else {
+        echo "Success.\n";
+    }
+}
+$conn->close();
+?>