Summary
This PR fixes a bug where images uploaded from a local device do not appear in the CMS preview pane. The preview now properly renders images by checking if the value is a File object and using URL.createObjectURL() to display it.

Closes #7576

Images uploaded from a user’s device were not showing in the preview pane, causing confusion even though the upload succeeded. This change fixes that by detecting local file uploads and using URL.createObjectURL() to display them instantly in the preview.

Test plan

• Cloned the repo locally on macOS
• Ran the project using npm install then npm start
• Opened an editable entry in the CMS demo
• Uploaded an image from my device
• Verified the image appeared in the preview without needing to save or refresh

Checklist

Please add a x inside each checkbox:

• [ x] I have read the contribution guidelines.

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