Surface the S5a media_kind discriminator in the library UI. A generic
uploaded file (media_kind='file') is download+share only — no player and
no timeline to trim, so Play/Edit/Edit-details are media-only; it shows a
neutral file glyph instead of an (always-empty) thumbnail and no duration
chip (container/size still read). The "Shared with me" tab's file row is
gated the same way. Re-download is now hidden for edit clips and uploads
too (neither has a re-fetchable source — the backend already rejects both
with 409), removing a latent click-to-409 on edit rows.
FE-only: the serializer already emits media_kind (S5a). Adds media_kind to
the DownloadAsset type and "upload" to the job_kind union; DOM tests cover
the file-row presentation (glyph, no img, no duration).
peter
b4ad59274b