feat(ajax): enhance request handling with callback support

The changes improve the AJAX request system by:

- Adding `onSuccess`, `onError`, and `onComplete` callback support
- Enhancing context handling and parameter merging
- Fixing typos and improving code comments
- Better error handling and response processing
- Adding delay support for AJAX requests
- Improving media browser and form handling
- Bumped version to `1.6.5`

Author: bkader