Update `HasThumbnail` in `fileViewWithReactions` to evaluate to true if the file already has a thumbnail or if it is a file type that requires one (`jobs.NeedsThumbnail`). This ensures the download page renders the thumbnail element for files that are pending thumbnail generation or support dynamic thumbnails.
Additionally, update tests in `upload_stage3_test.go` to verify the thumbnail image is rendered and relax the OG image URL matching.