[feature/validation-wrapping] Add note about the onFail return behavior

Clarified that the onFail callback will not trigger ValidationException if it returns false. This ensures better understanding for customizing validation failure handling and avoids potential issues in form submission.

docs/Handlers/ValidationHandler.md

@@ -149,6 +149,7 @@ class YourController extends Controller
                 ->onFail(function ($request, $errors) {
                     // Optional: Custom failure handling
                     // This will be called before the ValidationException is thrown
+                    // Unless you return false
                     Log::warning('Form submission failed', ['errors' => $errors->toArray()]);
                 })
                 ->finally(function ($request, $passed) {