✨ Refactor JavaScript controllers for improved readability and performance

- Replaced custom debounce function with lodash's debounce in entry_autosave_controller.js.
- Simplified OS detection logic in keyboard_shortcut_controller.js.
- Cleaned up formatting and removed unnecessary comments in form_validator_controller.js and writing_improver_controller.js.
- Ensured consistent use of single quotes and improved method definitions across controllers.