E5 S3: unified Plex card — scrim-reveal hover + rest polish

The poster card (grid + person page) gets the Seerr-style hover: on hover a
bottom scrim slides up with the title, a "year · runtime · ★rating" meta line,
and a 3-line synopsis — the info you'd otherwise click through for — plus a
less-flat play ring (radial-gradient + ring shadow) and a top-right quick-action
cluster (Info + watched-toggle, revealed on hover / always on touch). Rest-state
badges (season / type tag) yield to the scrim on hover; the playable-cost tint
stays. (§1 A + C from the enrichment study.)

Backend (the data the scrim needs, mirroring S1's `art`): the grid
(browse.unified_library) now emits a lang-coalesced, truncated `summary` (new
query.summary_col) + the Plex `rating`; movie_card/show_card do the same (EN) for
the detail/related/person cards. PlexCard.rating type added (summary already
existed for episodes).

Gate: tsc x3 / eslint / prettier / knip / vitest 326 green; ruff green; backend
lane full suite green. Self-E2E on the live dev server (rebuilt on this branch,
S2-enriched): the grid serves rating+summary (Shawshank 9.3, Godfather 9.2, real
synopses) and the card renders the play ring + scrim (The Expanse: ring, synopsis,
★8.1) — verified via the DOM (the pane wouldn't composite for a screenshot).

frontend/src/components/plexCards.dom.test.tsx

@@ -61,6 +61,26 @@ describe("PlexPosterCard a11y", () => {
     );
     expect(screen.getByRole("button", { name: "plex.markUnwatched" })).toBeTruthy();
   });
+
+  it("reveals the synopsis + rating on the hover scrim when the card carries them", () => {
+    render(
+      <PlexPosterCard
+        card={{ ...movie(), year: 2023, rating: 7.5, summary: "A quiet synopsis." }}
+        onOpen={vi.fn()}
+        onInfo={vi.fn()}
+        onToggleWatched={vi.fn()}
+      />,
+    );
+    expect(screen.getByText("A quiet synopsis.")).toBeTruthy();
+    expect(screen.getByText("7.5")).toBeTruthy(); // rating.toFixed(1)
+  });
+
+  it("omits the scrim when the card has no synopsis or rating", () => {
+    render(
+      <PlexPosterCard card={movie()} onOpen={vi.fn()} onInfo={vi.fn()} onToggleWatched={vi.fn()} />,
+    );
+    expect(screen.queryByText(/synopsis/i)).toBeNull();
+  });
 });
 
 describe("SeasonCard a11y", () => {