Verify email addresses

[evadecker]

Implement email verification during registration in order to combat spam, abuse, etc.

Email verification should also trigger when the user changes their email in settings.

A user should be able to log in and use the app without verifying, but we should display persistent notifications in settings and on their home page to encourage verification.

Follow the Convex Auth guide for setting up email verification using Resend: https://labs.convex.dev/auth/config/passwords#email-verification-setup