feat: implement order management and checkout functionality

- Added `Order` and `OrderItem` models with migrations for managing orders and their details
- Created `CheckoutForm` for validating order data and customer information
- Built templates for order confirmation, checkout success, and emails (HTML and plain text)
- Added logic for email notifications upon successful order placement
- Enhanced shopping cart template with checkout panel integration
- Updated styles and JavaScript for streamlined checkout UX
- Refactored cart view to support item summaries and final totals during checkout

templates/orders/success.html

@@ -0,0 +1,53 @@
+{% extends "_layouts/base.html" %}
+{% load static %}
+
+{% block title %}Оплата прошла успешно{% endblock %}
+
+{% block add_css %}
+    <link rel="stylesheet" href="{% static "css/cart.css" %}">
+{% endblock %}
+
+{% block content %}
+    {% include "_fragments/header.html" %}
+
+    {% include '_fragments/breadcrumbs.html' with url_1='/' text_1='Главная' url_2='/orders/cart/' text_2='Корзина' url_3=request.path text_3='Заказ оплачен' %}
+
+    <main class="container cart-page">
+        <section class="order-success">
+            <p class="order-success__eyebrow">Оплата прошла успешно</p>
+            <h1>Заказ №{{ order.id }} оформлен</h1>
+            <p class="order-success__lead">
+                Мы отправили письмо с деталями заказа на {{ order.email }}. Менеджер свяжется с вами при необходимости.
+            </p>
+
+            <div class="order-success__summary">
+                <div>
+                    <span>Получатель</span>
+                    <strong>{{ order.customer_name }}</strong>
+                </div>
+                <div>
+                    <span>Способ доставки</span>
+                    <strong>{{ order.get_delivery_method_display }}</strong>
+                </div>
+                <div>
+                    <span>Способ оплаты</span>
+                    <strong>{{ order.get_payment_method_display }}</strong>
+                </div>
+                <div>
+                    <span>Итого</span>
+                    <strong>{{ order.total }} руб.</strong>
+                </div>
+            </div>
+
+            <div class="order-success__items">
+                {% for item in order.items.all %}
+                    <p><span>{{ item.item_name }} × {{ item.quantity }}</span><strong>{{ item.line_total }} руб.</strong></p>
+                {% endfor %}
+            </div>
+
+            <a class="order-success__link" href="/catalog/">Вернуться в каталог</a>
+        </section>
+    </main>
+
+    {% include "_fragments/footer.html" %}
+{% endblock %}