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/PlexLibraryPicker.tsx

@@ -5,6 +5,7 @@ import { qk } from "../lib/queryKeys";
 import { api, type PlexCard } from "../lib/api";
 import { useDebounced } from "../lib/useDebounced";
 import { LoadingState } from "./ui/QueryState";
+import { cardImage } from "../lib/plexImage";
 
 // A debounced library search-and-pick list, shared by the "Add title" panel (PlexCollectionView) and
 // the "New collection" first-title panel (plexBrowseLists) — both search the library the same way and
@@ -49,7 +50,7 @@ export default function PlexLibraryPicker({
       {results.map((c) => (
         <li key={c.id} className="flex items-center gap-3">
           <img
-            src={c.thumb}
+            {...cardImage(c.thumb)}
             alt=""
             className="h-12 w-8 shrink-0 rounded object-cover"
             loading="lazy"