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.

migrations/Version20260711210000.php

@@ -0,0 +1,38 @@
+<?php
+
+declare(strict_types=1);
+
+namespace DoctrineMigrations;
+
+use Doctrine\DBAL\Schema\Schema;
+use Doctrine\Migrations\AbstractMigration;
+
+final class Version20260711210000 extends AbstractMigration
+{
+    public function getDescription(): string
+    {
+        return 'Add deleted_at and last_login_at to user table; cascade-delete email_log and reset_password_request rows';
+    }
+
+    public function up(Schema $schema): void
+    {
+        $this->addSql('ALTER TABLE `user` ADD deleted_at DATETIME DEFAULT NULL, ADD last_login_at DATETIME DEFAULT NULL');
+
+        $this->addSql('ALTER TABLE email_log DROP FOREIGN KEY FK_6FB4883A76ED395');
+        $this->addSql('ALTER TABLE email_log ADD CONSTRAINT FK_6FB4883A76ED395 FOREIGN KEY (user_id) REFERENCES `user` (id) ON DELETE CASCADE');
+
+        $this->addSql('ALTER TABLE reset_password_request DROP FOREIGN KEY FK_7CE748AA76ED395');
+        $this->addSql('ALTER TABLE reset_password_request ADD CONSTRAINT FK_7CE748AA76ED395 FOREIGN KEY (user_id) REFERENCES `user` (id) ON DELETE CASCADE');
+    }
+
+    public function down(Schema $schema): void
+    {
+        $this->addSql('ALTER TABLE email_log DROP FOREIGN KEY FK_6FB4883A76ED395');
+        $this->addSql('ALTER TABLE email_log ADD CONSTRAINT FK_6FB4883A76ED395 FOREIGN KEY (user_id) REFERENCES `user` (id)');
+
+        $this->addSql('ALTER TABLE reset_password_request DROP FOREIGN KEY FK_7CE748AA76ED395');
+        $this->addSql('ALTER TABLE reset_password_request ADD CONSTRAINT FK_7CE748AA76ED395 FOREIGN KEY (user_id) REFERENCES `user` (id)');
+
+        $this->addSql('ALTER TABLE `user` DROP deleted_at, DROP last_login_at');
+    }
+}