Image, album, and video bubbles in the official-assets category now
render the attachment filename as a bottom-left overlay so editors can
identify the source asset at a glance. Shared AttachmentFilenameLabel
component mirrors the AttachmentDownloadPill style, uses
filenameWithExtension so MIME-only attachments still get a sensible
label, and is pointer-events-none so it never blocks the bubble's tap
target.
