added migration seeders models and test script

app/Models/TodoCategoryModel.php

@@ -0,0 +1,57 @@
+<?php
+
+namespace App\Models;
+
+use CodeIgniter\Model;
+
+class TodoCategoryModel extends Model
+{
+    protected $table = 'todo_categories';
+    protected $primaryKey = 'todo_id'; // Composite primary key
+    protected $useAutoIncrement = false;
+    protected $returnType = 'array';
+    protected $useSoftDeletes = false;
+    protected $allowedFields = [
+        'todo_id',
+        'category_id',
+    ];
+
+    protected $useTimestamps = false;
+
+    // Add category to todo
+    public function addCategoryToTodo($todoId, $categoryId)
+    {
+        return $this->insert([
+            'todo_id' => $todoId,
+            'category_id' => $categoryId,
+        ]);
+    }
+
+    // Remove category from todo
+    public function removeCategoryFromTodo($todoId, $categoryId)
+    {
+        return $this->where('todo_id', $todoId)
+                    ->where('category_id', $categoryId)
+                    ->delete();
+    }
+
+    // Get categories for a todo
+    public function getCategoriesForTodo($todoId)
+    {
+        return $this->select('categories.*')
+                    ->join('categories', 'todo_categories.category_id = categories.id')
+                    ->where('todo_categories.todo_id', $todoId)
+                    ->get()
+                    ->getResultArray();
+    }
+
+    // Get todos for a category
+    public function getTodosForCategory($categoryId)
+    {
+        return $this->select('todos.*')
+                    ->join('todos', 'todo_categories.todo_id = todos.id')
+                    ->where('todo_categories.category_id', $categoryId)
+                    ->get()
+                    ->getResultArray();
+    }
+}