added pasting of images and correct image format handling

[danieltallentire]

This pull request includes enhancements to handle image uploads more effectively in the chat application. The changes primarily focus on capturing and processing the media type of images, as well as handling pasted images in the chat interface.

Enhancements to image handling:

• app.py: Added support to capture the media type of images from the request data and use it when creating the message content.

• static/js/chat.js:

  • Added an event listener to handle pasted images, convert them to base64, and update the preview with the correct media type.
  • Modified the image preview in the chat to use the correct media type when displaying images.
  • Updated the form submission to include the media type of the image in the request payload.