perf(series): list a series' episodes with one concurrent season walk

"More info" on Frasier took ~10 s. The series page asked Rust for the
episodes and for the current episode as two commands; each walked every
season, and each walk fetched the eleven seasons one after another. So the
wait was the sum of twenty-two listings, each a cache read queued behind
whatever the database was writing — measured at ~4 s per walk on a Fairphone
5 while the launch-time catalog sync ran.

Seasons are now fetched together (gather_season_episodes), so a walk waits
for its slowest season, not the sum. And repository_get_series_view returns
the episodes and the current episode from one walk, with Next Up and resume
fetched alongside it; the series page makes that one call.

Under today's single database connection the cache reads themselves still
queue on its mutex; the concurrency pays off fully once reads get their own
connections. Halving the walks helps regardless.

Test first: ten 100 ms seasons took 1.01 s sequentially; now well under the
400 ms bound, with a failing season still leaving the rest.

DR-295, UT-264.

src/lib/api/bindings.ts

@@ -1590,6 +1590,16 @@ async repositoryGetSeriesEpisodes(handle: string, seriesId: string) : Promise<Me
 async repositoryGetSeriesCurrentEpisode(handle: string, seriesId: string) : Promise<MediaItem | null> {
     return await TAURI_INVOKE("repository_get_series_current_episode", { handle, seriesId });
 },
+/**
+ * A series' episodes and the viewer's current episode, from one season
+ * fan-out. The series page used to ask for these as two commands, each of
+ * which walked every season.
+ * 
+ * TRACES: UR-062 | DR-101, DR-295
+ */
+async repositoryGetSeriesView(handle: string, seriesId: string) : Promise<SeriesView> {
+    return await TAURI_INVOKE("repository_get_series_view", { handle, seriesId });
+},
 /**
  * Erase the viewer's watch history for an item.
  * 
@@ -3445,6 +3455,16 @@ export type SecurityStatus = { usingKeyring: boolean; storageType: string }
  * Audio track preference for a series
  */
 export type SeriesAudioPreference = { seriesId: string; audioTrackDisplayTitle: string | null; audioTrackLanguage: string | null; audioTrackIndex: number | null }
+/**
+ * A series' episodes and the one the viewer is up to, from **one** season
+ * fan-out.
+ * 
+ * The series page needs both, and asked for them as two commands; each walked
+ * every season, so every visit listed the show twice. One call, one walk.
+ * 
+ * TRACES: UR-062 | DR-101, DR-295
+ */
+export type SeriesView = { episodes: MediaItem[]; current: MediaItem | null }
 /**
  * The verdict on a server's version.
  *