Send confirmation email to activate account

[hyunbin7303]

Overview

Implement a feature to send a confirmation email to users after they sign up, requiring them to confirm their email address in order to activate their account.

Requirements

• Generate a unique activation token for each new account
• Send a confirmation email with an activation link to the user's email address
• Handle the activation link route to activate the account when clicked
• Handle expired or invalid tokens gracefully

Acceptance Criteria

• A confirmation email is sent automatically upon user registration
• The activation link properly activates user accounts
• Prevent login until the account is activated
• Provide user-friendly error messages for expired/invalid links

Notes

• This will help prevent spam and ensure only valid email addresses are registered.