++ fix: use months for assignment PDF link TTL instead of hours

app/Models/Setting.php

@@ -6,6 +6,8 @@ use Illuminate\Database\Eloquent\Model;
 
 class Setting extends Model
 {
+    protected static ?self $cachedInstance = null;
+
     protected $fillable = [
         'congregazione_nome',
         'logo_path',
@@ -13,6 +15,7 @@ class Setting extends Model
         'giorni_giacenza_prioritari',
         'giorni_per_smarrito',
         'home_limit_list',
+        'assignment_link_ttl_hours',
         'audit_retention_days',
         'setup_completed',
     ];
@@ -25,22 +28,41 @@ class Setting extends Model
             'giorni_giacenza_prioritari' => 'integer',
             'giorni_per_smarrito' => 'integer',
             'home_limit_list' => 'integer',
+            'assignment_link_ttl_hours' => 'integer',
             'audit_retention_days' => 'integer',
         ];
     }
 
+    protected static function booted(): void
+    {
+        static::saved(function (): void {
+            static::$cachedInstance = null;
+        });
+
+        static::deleted(function (): void {
+            static::$cachedInstance = null;
+        });
+    }
+
     /**
      * Get the singleton settings instance (first row).
      */
     public static function instance(): static
     {
-        return static::firstOrCreate([], [
+        if (static::$cachedInstance instanceof static) {
+            return static::$cachedInstance;
+        }
+
+        static::$cachedInstance = static::firstOrCreate([], [
             'giorni_giacenza_da_assegnare' => 120,
             'giorni_giacenza_prioritari' => 180,
             'giorni_per_smarrito' => 120,
             'home_limit_list' => 10,
+            'assignment_link_ttl_hours' => 1,
             'audit_retention_days' => 730,
         ]);
+
+        return static::$cachedInstance;
     }
 
     public static function isSetupComplete(): bool