feat: implement module purchase dialog with subscription type selection, auto-renew, and dependency checks, replacing the dedicated purchase page.

src/backend/Zentral.API/Controllers/ModulesController.cs

@@ -244,7 +244,7 @@ public class ModulesController : ControllerBase
             Dependencies = module.GetDependencies().ToList(),
             RoutePath = module.RoutePath,
             IsAvailable = module.IsAvailable,
-            IsEnabled = module.IsCore || (module.Subscription?.IsValid() ?? false),
+            IsEnabled = module.IsCore || ((module.Subscription?.IsEnabled ?? false) && (module.Subscription?.IsValid() ?? false)),
             Subscription = module.Subscription != null ? MapSubscriptionToDto(module.Subscription) : null
         };
     }

src/backend/Zentral.API/Services/ModuleService.cs

@@ -87,7 +87,7 @@ public class ModuleService
         if (module.IsCore)
             return true;
 
-        return module.Subscription?.IsValid() ?? false;
+        return (module.Subscription?.IsEnabled ?? false) && (module.Subscription?.IsValid() ?? false);
     }
 
     /// <summary>
@@ -200,7 +200,7 @@ public class ModuleService
 
         // Verifica se altri moduli dipendono da questo
         var dependentModules = await GetDependentModulesAsync(code);
-        var activeDependents = dependentModules.Where(m => m.Subscription?.IsValid() ?? false).ToList();
+        var activeDependents = dependentModules.Where(m => (m.Subscription?.IsEnabled ?? false) && (m.Subscription?.IsValid() ?? false)).ToList();
         if (activeDependents.Any())
             throw new InvalidOperationException(
                 $"I seguenti moduli attivi dipendono da questo modulo: {string.Join(", ", activeDependents.Select(m => m.Name))}");

src/backend/Zentral.Domain/Entities/ModuleSubscription.cs

@@ -72,9 +72,6 @@ public class ModuleSubscription : BaseEntity
     /// </summary>
     public bool IsValid()
     {
-        if (!IsEnabled)
-            return false;
-
         // Se non c'è data di scadenza, è valido (licenza perpetua o core module)
         if (!EndDate.HasValue)
             return true;