Reuse the existing UUID trait instead of a second copy of the logic

Mailbox hand-rolled the same creating-time UUID assignment that
App\Models\Concerns\HasUuid already provides to 17 other models under
R11 (URLs address records by UUID, not integer PK), and skipped the
route-key binding that comes with it. Swap onto the trait, and cover
both the assignment and the route key with a test matching the
convention already used for Host/Order.

Also match MailboxFactory's @extends annotation to how the other
factories in the repo write it (Pint's fully_qualified_strict_types
rule turns a fully-qualified docblock reference into an import plus a
short name anyway, so this is what it would end up as either way).

app/Models/Mailbox.php

@@ -2,10 +2,10 @@
 
 namespace App\Models;
 
+use App\Models\Concerns\HasUuid;
 use App\Services\Secrets\SecretCipher;
 use Illuminate\Database\Eloquent\Factories\HasFactory;
 use Illuminate\Database\Eloquent\Model;
-use Illuminate\Support\Str;
 
 /**
  * One sending address.
@@ -16,7 +16,7 @@ use Illuminate\Support\Str;
  */
 class Mailbox extends Model
 {
-    use HasFactory;
+    use HasFactory, HasUuid;
 
     protected $fillable = [
         'key', 'address', 'display_name', 'username',
@@ -32,13 +32,6 @@ class Mailbox extends Model
         ];
     }
 
-    protected static function booted(): void
-    {
-        static::creating(function (self $box) {
-            $box->uuid ??= (string) Str::uuid();
-        });
-    }
-
     public static function findByKey(string $key): ?self
     {
         return static::query()->where('key', $key)->first();

database/factories/MailboxFactory.php

@@ -2,8 +2,10 @@
 
 namespace Database\Factories;
 
+use App\Models\Mailbox;
 use Illuminate\Database\Eloquent\Factories\Factory;
 
+/** @extends Factory<Mailbox> */
 class MailboxFactory extends Factory
 {
     public function definition(): array

tests/Feature/Mail/MailboxModelTest.php

@@ -39,3 +39,10 @@ it('finds a mailbox by its key', function () {
     expect(Mailbox::findByKey('billing'))->not->toBeNull()
         ->and(Mailbox::findByKey('gibtsnicht'))->toBeNull();
 });
+
+it('auto-assigns a uuid and routes by it', function () {
+    $box = Mailbox::factory()->create();
+
+    expect($box->uuid)->not->toBeNull()
+        ->and($box->getRouteKeyName())->toBe('uuid');
+});