Refactor email system and add contact form backend

Refactored email sending to use a single HTML template with a base layout, removed plain text email templates, and updated all related backend logic. Introduced a new ContactMe model, serializer, Celery task, and API endpoints for handling contact form submissions, including email notifications. Renamed ShopConfiguration to SiteConfiguration throughout the backend for consistency. Updated frontend to remove unused components, add a new Services section, and adjust navigation and contact form integration.

backend/advertisement/serializer.py

@@ -0,0 +1,9 @@
+from rest_framework import serializers
+from .models import ContactMe
+
+
+class ContactMeSerializer(serializers.ModelSerializer):
+    class Meta:
+        model = ContactMe
+        fields = ["id", "client_email", "content", "sent_at"]
+        read_only_fields = ["id", "sent_at"]