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

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))}");