Move the v2 upgrade token migration to its own version

Diesel identifies a migration by the date in its folder name alone, and silently drops one of two folders that share it. The Custom Roles migration uses the same date.

migrations/postgresql/2026-11-04-120000_add_v2_upgrade_token/down.sql

@@ -0,0 +1,2 @@
+ALTER TABLE users DROP COLUMN v2_upgrade_token;
+ALTER TABLE users_organizations DROP COLUMN v2_upgrade_token;