Replace IdentityNoOpEmailSender with a real implementation and remove any UI fallbacks in account pages.

[connorjamessmith]

The body includes HTML links; ensure the real sender sets the content type to HTML. With the no-op, it’s moot, but keep it in mind when swapping implementations.
There’s a helpful TODO in the file about removing a defensive UI branch once a real sender is plugged in—good practice.
When you wire a real IEmailSender, scan RegisterConfirmation.razor and related pages to remove any no-op logic branches.