feat: implement letter encryption fields, lifecycle timestamps, and API endpoints with validation

backend/letters/views.py

@@ -1 +1,15 @@
-# Create your views here.
+from rest_framework import generics
+from rest_framework.permissions import IsAuthenticated
+
+from letters.models import Letter
+from letters.serializers import LetterSerializer
+
+
+class LetterView(generics.ListCreateAPIView):
+    serializer_class = LetterSerializer
+    # enforce auth guard
+    permission_classes = [IsAuthenticated]
+
+    def get_queryset(self):
+        """return only letters of the authenticated user"""
+        return Letter.objects.filter(user=self.request.user)