Issue #3541842: Refactor to remove unnecessary parent class inheritance
- Remove unnecessary ControllerBase inheritance from MarkdownController classes
- Replace FormBase inheritance with FormInterface + StringTranslationTrait in DifyWidgetOfficialConfigForm
- Fix DifyWidgetVanillaBlock access method to use blockAccess() instead of access()
- Implement proper dependency injection with ContainerInjectionInterface
- Follow Drupal 11 coding standards and best practices
Closes #3541842