feat: send email notification on account hard-delete

Notify users via email when their account is permanently deleted after
the 15-day soft-delete grace period. Query now returns email alongside
user ID so the notification can be sent after deletion.

Email failure is logged as a warning but does not block cleanup.

db/queries/users.sql

@@ -92,7 +92,7 @@ WHERE ut.user_id = $1
   );
 
 -- name: ListExpiredSoftDeletedUsers :many
-SELECT id FROM users WHERE deleted_at IS NOT NULL AND deleted_at < NOW() - INTERVAL '15 days';
+SELECT id, email FROM users WHERE deleted_at IS NOT NULL AND deleted_at < NOW() - INTERVAL '15 days';
 
 -- name: HardDeleteUser :exec
 DELETE FROM users WHERE id = $1;