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/lib/api/plex.ts

@@ -43,6 +43,7 @@ export interface PlexCard {
   duration_seconds?: number | null;
   thumb: string;
   art?: string | null; // wide backdrop (movies/shows) for rails + crossfading hero; null when no art_key
+  rating?: number | null; // Plex audience score (~IMDb), shown on the card hover-overview
   playable?: string; // direct | remux | transcode
   status?: string; // new | watched | hidden
   position_seconds?: number;
@@ -51,7 +52,7 @@ export interface PlexCard {
   episode_number?: number | null; // episode
   show_title?: string | null; // episode (in a mixed playlist)
   show_id?: string | null; // episode: the show's rating_key (for grouping a playlist by show/season)
-  summary?: string | null; // episode
+  summary?: string | null; // movie/show hover-overview synopsis (trimmed) + episode summary
 }
 // Unified cross-library browse (movies + shows mixed). `episodes` is populated only on a search that
 // also matches episodes (the grouped "Episodes" section).