Require two-factor authentication for admins and supervisors

Admins and supervisors without 2FA are sent a code at their next login,
and verifying it turns 2FA on. They can change the channel but not turn
it off. Older sessions without 2FA are rejected with TWO_FACTOR_REQUIRED,
and promoting a user ends their sessions so they enrol at next login.
The requirement is skipped when no email or WhatsApp channel can deliver
a code, and TWO_FACTOR_REQUIRED_ROLES=false switches it off.

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

backend/src/controllers/settingsController.js

@@ -172,7 +172,9 @@ const setupRegister = async (req, res) => {
       },
     });
 
-    const token = generateToken(user.id, user.role, user.tokenVersion ?? 0);
+    // Marked as a setup token so the 2FA requirement doesn't block the rest of the
+    // wizard; the admin enrols at their first normal login.
+    const token = generateToken(user.id, user.role, user.tokenVersion ?? 0, { setup: true });
     res.json({ token, name: user.name, email: user.email });
   } catch (e) {
     res.status(res.statusCode === 200 ? 400 : res.statusCode).json({ message: safeErrorMessage(e) });