Static thumbnails in existing asset cells

The changed CreativeThumbnail component renders synthetic fixtures here. This is a component preview, not the full Whiskers app or a backend integration test. Next Image is replaced by a static image adapter.

Creative	Source	Asset	Expected behavior	Trends
Example image asset	Meta		Image variant	View trends
Example video asset	Meta		Resolved thumbnail image; no player	View trends
Example missing media	Meta	▧	Placeholder	View trends
Example other platform	Google	▧	Placeholder	View trends

Thumbnails are passive: no link, external-link arrow, player, or modal.