fix(plex): every small Plex picture asks for its card-size cut

The playlist rows, the search box and the collection picker still
fetched the 400px poster for a 32-80px picture. A contract test pins the
set of bare Plex pictures, and the srcset widths to imgcache.SIZES.

frontend/src/components/PlexSearchBox.tsx

@@ -12,6 +12,7 @@ import { availablePlexFields, healPlexField, plexFieldLabelKey } from "../lib/pl
 import { Pressable } from "./ui/Pressable";
 import { SURFACE } from "./ui/surfaces";
 import { ROVING_HIGHLIGHT } from "./ui/AnchoredPopover";
+import { cardImage } from "../lib/plexImage";
 
 // The Plex header search box: the shared SearchBar enriched with the S2 search scope-pill (a
 // GitHub-style field selector inside the box) and an instant typeahead of the top matches attached
@@ -160,7 +161,7 @@ export default function PlexSearchBox() {
                   className={`flex w-full items-center gap-3 rounded-lg p-1.5 transition ${ROVING_HIGHLIGHT}`}
                 >
                   <img
-                    src={c.thumb}
+                    {...cardImage(c.thumb)}
                     alt=""
                     loading="lazy"
                     className="h-12 w-8 shrink-0 rounded-md object-cover bg-border/40"