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")

shell.nix

@@ -8,6 +8,7 @@ let
     argon2-cffi
     pyjwt
     cryptography
+    jinja2
   ]);
 in
 with pkgs;
@@ -20,6 +21,5 @@ mkShell {
     python313Packages.python-lsp-server
     python313Packages.jedi-language-server
     ty
-    ffmpeg
   ];
 }