feat: implement encrypted image support for letters with backend storage

backend/letters/views.py

@@ -1,7 +1,7 @@
 from rest_framework import generics
 from rest_framework.permissions import IsAuthenticated
 
-from letters.models import Letter
+from letters.models import Letter, LetterImage
 from letters.serializers import LetterSerializer
 
 
@@ -13,3 +13,9 @@ class LetterView(generics.ListCreateAPIView):
     def get_queryset(self):
         """return only letters of the authenticated user"""
         return Letter.objects.filter(user=self.request.user)
+
+    def perform_create(self, serializer):
+        letter = serializer.save(user=self.request.user)
+        image_files = self.request.FILES.getlist("image_files")
+        for image_file in image_files:
+            LetterImage.objects.create(letter=letter, file=image_file, file_name=image_file.name)