Add in a mechanism for email confirmation

This is some of the way there but it is still missing at least:
- An actual page to view to confirm the email
- An expiry time on the minted JWT (and other JWT issues like "sub")

derivation.nix

@@ -3,7 +3,7 @@ with python313Packages;
 buildPythonApplication {
   pname = "cereal";
   version = "0.0.1";
-  propagatedBuildInputs = [ flask requests waitress sqlalchemy argon2-cffi pyjwt cryptography];
+  propagatedBuildInputs = [ flask requests waitress sqlalchemy argon2-cffi pyjwt cryptography jinja2];
   src = ./.;
   pyproject = true;
   build-system = [setuptools];