Disable “Import to Canvas” Button Until Upload Completes #1245

Is your feature request related to a problem? Please describe.
During file uploads, the “Import to Canvas” button remains clickable. If a user clicks it prematurely, it may result in failed imports, empty data nodes, or system errors.

Describe the solution you'd like
Disable the “Import to Canvas” button during uploads and display an upload progress indicator. Once the upload completes, re-enable the button. If the upload fails, display an error message.

Additional context
This improvement would significantly reduce workflow interruptions caused by accidental clicks, especially when uploading large files.