Add Editable Context Windows in UI

[cosineai]

This PR implements the ability to edit and save context windows directly from the UI. Users can now modify the content of context windows in place and save the changes. The changes include:

1. A new script in the HTML to handle the save operation by sending a POST request with the updated content.
2. A new endpoint in the server to handle the save request, update the context window content, and write the changes to the context_windows.jsonl file.

These changes address the need for an editable and savable context window feature, enhancing the user experience by allowing in-place content updates.