Upgrade Django 4.0.10 -> 4.1.13

We also clear staticfiles as part of the build target.  When changing
Django version the format of manifest files can change so we want to be
robust against this situation.

Author: ghickman

Makefile

@@ -20,6 +20,7 @@ mypy:
 
 build: _uv
 	uv pip install -r requirements.prod.txt -r requirements.dev.txt
+	rm -rf staticfiles/*
 	python manage.py collectstatic --no-input
 	rm -f ccbv.sqlite
 	python manage.py migrate

requirements.prod.txt

@@ -18,7 +18,7 @@ dj-database-url==0.5.0
     # via environs
 dj-email-url==1.0.6
     # via environs
-django==4.0.10
+django==4.1.13
     # via
     #   -r requirements.prod.in
     #   django-extensions