Add passkey option on TOTP page and auto-trigger passkey for TOTP users

When a user has both passkeys and TOTP configured, auto-trigger the
passkey flow on login to save them from the password→TOTP path. Also
add a "Use Passkey Instead" button on the TOTP verification page as
an escape hatch for users who end up there.

Co-Authored-By: Claude Opus 4.6 <noreply@anthropic.com>

app/controllers/sessions_controller.rb

@@ -147,6 +147,10 @@ class SessionsController < ApplicationController
       nil
     end
 
+    # Pass data to the view for passkey option
+    @user_has_webauthn = user&.can_authenticate_with_webauthn?
+    @pending_email = user&.email_address
+
     # Just render the form
   end