feat(plex): Collection info page — hero, play/shuffle, and write-through editing (B)

Clicking a collection tile now opens a dedicated Collection info page (like the Plex-web
one) instead of just applying it as a filter. New GET /collections/{rk} returns the hero
aggregates (year range, most-restrictive member cert, total runtime) + the members ordered
by release year then title; a new PlexCollectionView renders the hero (art/title/meta/
summary+More) and the member grid, with a Play-all and Shuffle over the playable leaves
(reusing the player's existing queue + auto-advance).

For a non-external, admin-enabled collection the page offers rename / delete / add-title
(a search picker) / remove-item, all through the pre-existing admin endpoints that write
THROUGH to Plex (each edit awaits and re-fetches — no optimism, since a Plex write can 422).
An eligible collection shows "Enable editing" first (the DB editable flag). Read-only ones
(smart / imdb / tmdb / … auto-lists) are marked with a lock on both the info page AND the
browse tile, up front.

New `{ kind: "collection" }` sub-view wired through plexSubUrl (bookmarkable ?v=collection:rk),
PlexBrowse (render branch, Backspace back-nav, tile handler), with a round-trip test.

Verified live: tile→page, hero + chronological members (James Bond 1962→2021, PG-13, 55h),
Play/Shuffle, Enable editing → edit controls + remove-X, the add search (marks already-in
titles "Added"), and the read-only lock on external collections. Real Plex mutations wired
but not executed against the live account.

Gate: tsc/lint/knip/prettier clean, 424 vitest; backend ruff clean, 6 collections tests
(+ a detail-hero/ordering assertion).

frontend/src/components/PlexBrowse.tsx

@@ -42,6 +42,7 @@ import { PlexInfoView, PlexPersonView, PlexSeasonView, PlexShowView } from "./pl
 // Lazy: the rich player (pulls in hls.js) loads only when something is first played.
 const PlexPlayer = lazy(() => import("./PlexPlayer"));
 const PlexPlaylistView = lazy(() => import("./PlexPlaylistView"));
+const PlexCollectionView = lazy(() => import("./PlexCollectionView"));
 
 // The Plex module's content area: browse/search the mirrored library as poster cards, drill from a
 // show into seasons/episodes. Library scope / watch-state / sort live in the left PlexSidebar; the
@@ -173,6 +174,7 @@ export default function PlexBrowse() {
           "info",
           "person",
           "playlist",
+          "collection",
         ].includes(sub.view.kind)
       ) {
         e.preventDefault();
@@ -341,6 +343,20 @@ export default function PlexBrowse() {
       </Suspense>
     );
   }
+  if (sub.view.kind === "collection") {
+    const cid = sub.view.id;
+    return (
+      <Suspense fallback={<p className="p-8 text-muted text-sm">{t("plex.loading")}</p>}>
+        <PlexCollectionView
+          collectionId={cid}
+          onBack={sub.back}
+          onPlay={(rk, queue) => sub.open({ kind: "player", id: rk, queue })}
+          onOpenCard={onCard}
+          onInfoCard={onInfo}
+        />
+      </Suspense>
+    );
+  }
   if (sub.view.kind === "info") {
     const infoId = sub.view.id;
     return (
@@ -431,11 +447,7 @@ export default function PlexBrowse() {
   if (sub.view.kind === "collections") {
     return (
       <div className="p-4 max-w-[1600px] mx-auto">
-        <PlexCollectionsBrowse
-          onPick={(id, title) =>
-            applyFilter({ collections: [id], collectionTitles: { [id]: title } })
-          }
-        />
+        <PlexCollectionsBrowse onPick={(id) => sub.open({ kind: "collection", id })} />
       </div>
     );
   }