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/Entity/User.php

@@ -42,6 +42,12 @@ class User implements UserInterface, PasswordAuthenticatedUserInterface
     #[ORM\Column(type: 'boolean')]
     private bool $marketingOptIn = false;
 
+    #[ORM\Column(type: 'datetime_immutable', nullable: true)]
+    private ?\DateTimeImmutable $deletedAt = null;
+
+    #[ORM\Column(type: 'datetime_immutable', nullable: true)]
+    private ?\DateTimeImmutable $lastLoginAt = null;
+
     public function getId(): ?int
     {
         return $this->id;
@@ -152,4 +158,33 @@ class User implements UserInterface, PasswordAuthenticatedUserInterface
 
         return $this;
     }
+
+    public function getDeletedAt(): ?\DateTimeImmutable
+    {
+        return $this->deletedAt;
+    }
+
+    public function setDeletedAt(?\DateTimeImmutable $deletedAt): static
+    {
+        $this->deletedAt = $deletedAt;
+
+        return $this;
+    }
+
+    public function isDeleted(): bool
+    {
+        return $this->deletedAt !== null;
+    }
+
+    public function getLastLoginAt(): ?\DateTimeImmutable
+    {
+        return $this->lastLoginAt;
+    }
+
+    public function setLastLoginAt(?\DateTimeImmutable $lastLoginAt): static
+    {
+        $this->lastLoginAt = $lastLoginAt;
+
+        return $this;
+    }
 }