feat(verification): add image and video preview thumbnails after upload selection (#426)

[delightonyedikachipixel]

Summary

This PR resolves #426 by enhancing the MediaUploadStep component to display immediate visual previews of selected files before the user proceeds to the next step. This provides necessary visual feedback, assuring users that they have selected the correct media.

Changes Made

• Image Previews: Leveraged the DOM URL.createObjectURL() API to securely and efficiently generate local previews for selected image files.
• Video Previews: Implemented logic to extract the first frame of selected video files, gracefully falling back to a dedicated video icon if frame extraction is not immediately available.
• Component Update: Integrated the preview UI and conditional rendering logic directly into frontend/features/verification/components/steps/MediaUploadStep.tsx.

Acceptance Criteria Met

• Thumbnails render correctly immediately after file selection.
• Local object URLs are successfully generated for images.
• Video files correctly display either an extracted first frame or an icon.

Closes #426

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