Signals Notebook: PowerPoint preview missing graphics

Description

Missing graphics in the PowerPoint preview within the application. 

Solution

- Verify the issue across browsers (Chrome, Edge, Firefox) and profiles/private mode to rule out cache or extensions.
- Confirm image download and site permissions are allowed in the browser (images, automatic downloads).
- Test the same PPTX on another machine/account to confirm it is not user-specific.
- If graphics remain missing, replace SVG objects in the PowerPoint with PNG bitmaps and re-upload to the application.
- Alternatively, save the presentation as an older PowerPoint format (e.g., .ppt) and test the preview again.
- Re-upload the adjusted file and confirm the preview renders correctly.