Add two-factor login (TOTP) with recovery codes

Users can set up an authenticator app from their account page; login
then asks for a code after the password, with one-time recovery codes
as a fallback. Sensitive actions (tokens, user changes, 2FA resets)
need a code from the last 5 minutes. totp.require (none/admins/all)
forces setup, and admins can reset a user's 2FA from the UI, the jarl
CLI or jarld on the server. The dashboard and jarl status flag users
missing 2FA and a shared "admin" account still in use.

Co-Authored-By: Claude Opus 5.5 <noreply@anthropic.com>

docs/operations.md

@@ -218,6 +218,7 @@ socket, without a token.
 | Forgot the admin password | `sudo jarl user update admin --password`, or (also with jarld stopped) `sudo -u jarl jarld user passwd admin` |
 | Locked out by the login rate limit | wait 15 minutes, or `systemctl restart jarl` (the limiter is in memory) |
 | Lost every admin account | `sudo -u jarl jarld user add --admin rescue` |
+| Lost the phone with the authenticator app, and the recovery codes | another administrator: Users → Reset 2FA, or `jarl user totp reset NAME`; on the server: `sudo -u jarl jarld user totp reset NAME` |
 | Need a token without the web UI | `sudo jarl token create cli --user admin`, or `sudo -u jarl jarld user token admin cli` |
 
 ## A secondary server