R1:4f8d07594e2a

Fix a CSRF issue with adding new email addresses

Summary:
The first dialog was being given the wrong user (`$user`, should be `$viewer`), leading to a CSRF issue.

(The CSRF token it generated was invalid in all validation contexts, so this wasn't a security problem or a way to capture CSRF tokens for other users.)

Use `newDialog()` instead.

(This seems completely unrelated to the vaguely-similar-looking issues we saw earlier this week.)

Test Plan:
- Added a new email address.
- Clicked "Done" on…