Reset selected email session value on email deletion

[aduth]

🛠 Summary of changes

Updates email deletion behavior to reset user session value for selected email preference.

This fixes an unlikely user path which could result in an unhandled 500 error.

📜 Testing Plan

1. Prerequisite: Have an account with multiple email addresses
2. Prerequisite: Disconnect from sample application if already consented, from "Connected Accounts" account page
3. Run sample application in separate process from IdP
4. Go to http://localhost:9292
5. Click "Sign in"
6. Complete sign-in up to consent screen
7. Click "Change" next to email address
8. Select an email address. Remember which email you selected.
9. Click "Change"
10. In a separate tab, go to http://localhost:3000
11. From account dashboard, delete (and confirm deletion of) the email you selected on Step 8
12. Return to the original tab for the partner attributes consent screen
13. Refresh the page

Before: You'd encounter a ActiveRecord::RecordNotFound 500 error
After: The consent screen loads, and the email address is reset to the default value (what you'd seen at Step 6)