fix(design): an audit of the S3d claims — the float shadow, filter hints, one action size per row (E28 S3d)

- A glass role's shadow is one token (shadow-float); the header search's drop-shadow utility had
  replaced its top highlight, and the debug pill's shadow-lg did the same. The surface-role lint
  rule now refuses a shadow size beside a role.
- Plex: every value that filters carries a hint (genre, certificate, studio had none), and the facts
  panel's year and certificate filter like the header's. filterKeyword -> filterValue.
- Downloads: the row resized its buttons with a [&_button] override that the save link escaped
  (28px beside 32px); the size is the primitive's md rung now.

frontend/src/components/DownloadCenter.tsx

@@ -160,7 +160,7 @@ export default function DownloadCenter() {
   if (!tabs.some((tb) => tb.id === tab)) setTab("queue");
 
   const saveBtn = (job: DownloadJob) => (
-    <IconLink href={api.downloadFileUrl(job.id)} label={t("downloads.actions.download")}>
+    <IconLink href={api.downloadFileUrl(job.id)} label={t("downloads.actions.download")} size="md">
       <Download />
     </IconLink>
   );