The Vault page already shows file drops and stored mail (e3ddeb0) but
the inspector drawer had no download button — only the live-feed
ArtifactDrawer/MailDrawer offered raw byte retrieval. Add a DOWNLOAD
RAW action to BountyInspector that fires when bounty_type=artifact,
hitting /artifacts/{decky}/{stored_as}?service=<svc> with the bounty's
own service field (ssh or smtp). Mirrors ArtifactDrawer's blob handling
and 400/403/404 error mapping.
Also widen the icon/label vocabulary: artifact bounties get FileText
(file drops) or Mail (message_stored) instead of the generic Package,
and the inspector header chip mirrors the change.
