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/downloadRow.tsx

@@ -141,6 +141,7 @@ export function IconBtn({
   return (
     <IconButton
       variant={danger ? "danger" : "ghost"}
+      size="md"
       onClick={onClick}
       data-nav-open={open ? "" : undefined}
       label={title}
@@ -304,7 +305,7 @@ export function DownloadRow({
       {/* Row action buttons: the md rung here (the row stands alone), the sm rung in the modals, one
           IconBtn for both. `shrink-0` + no wrap keeps them on the title's line; the text column
           shrinks instead. */}
-      <div className="flex items-start gap-1 shrink-0 [&_button]:size-8">{children}</div>
+      <div className="flex items-start gap-1 shrink-0">{children}</div>
     </div>
   );
 }