Soft-delete users instead of hard-deleting, add last login tracking

Fixes the 500 on admin user deletion: deleting a user with an
email_log row (i.e. basically anyone who received any email) hit an
unhandled ForeignKeyConstraintViolationException, since email_log,
reset_password_request and player all have non-nullable FKs to user
with no cascade at the DB level.

Instead of cascading the delete (which would be fine for email_log
and reset_password_request but risky for player - removing a player
row could corrupt other real players' session state), admin delete
now sets a deletedAt timestamp instead of removing the row:
- UserChecker blocks login for deleted users (checkPreAuth).
- EmailLoggerListener rejects the message before send for deleted
  recipients (checked at actual send time, not at queue time).
- Added a last_login_at column + a LoginSuccessEvent listener to
  populate it, and surfaced both last login and status in the admin
  users list.

Added `app:users:purge-deleted`, a command intended to run on a
schedule that permanently removes users who were soft-deleted more
than 3 months ago and never played a game (join to Player via a
NOT EXISTS subquery). For that eventual hard-delete to actually
succeed, email_log and reset_password_request now cascade-delete at
the DB level (migration drops+recreates both FK constraints with ON
DELETE CASCADE) - player intentionally still isn't cascaded, so a
user with game history can never be purged this way even by mistake.

src/Tech/Repository/UserRepository.php

@@ -44,4 +44,20 @@ class UserRepository extends ServiceEntityRepository implements PasswordUpgrader
             ->getQuery()
             ->getResult();
     }
+
+    /**
+     * Soft-deleted users, deleted before the given date, who never played a game.
+     *
+     * @return User[]
+     */
+    public function findPurgeableDeletedUsers(\DateTimeImmutable $deletedBefore): array
+    {
+        return $this->createQueryBuilder('u')
+            ->andWhere('u.deletedAt IS NOT NULL')
+            ->andWhere('u.deletedAt <= :deletedBefore')
+            ->andWhere('NOT EXISTS (SELECT 1 FROM App\Game\Entity\Player p WHERE p.user = u)')
+            ->setParameter('deletedBefore', $deletedBefore)
+            ->getQuery()
+            ->getResult();
+    }
 }