fix: update dockerfile paths in docker-compose and fly.toml for backend service

apps/backend/fly.toml

@@ -7,7 +7,7 @@ app = "classroomio-server"
 primary_region = "lhr"
 
 [build]
-  dockerfile = "Dockerfile.prod"
+  dockerfile = "Dockerfile"
 
 [http_service]
   internal_port = 3002

docker-compose.yaml

@@ -9,8 +9,8 @@ version: '3.8'
 services:
   backend:
     build:
-      context: ./apps/backend
-      dockerfile: Dockerfile
+      context: .
+      dockerfile: ./apps/backend/Dockerfile
       args:
         - PUBLIC_SUPABASE_ANON_KEY=${PUBLIC_SUPABASE_ANON_KEY}
         - PUBLIC_SUPABASE_URL=${PUBLIC_SUPABASE_URL}