Series drill-down: season posters

The drill-down reads the series with includeSeasonImages=true (Sonarr
only sends season posters when asked, as TheTVDB links). A selected
season or episode shows its season's poster; without one, or when it
cannot be loaded, the series poster.

Co-Authored-By: Claude Opus 5.5 <noreply@anthropic.com>

internal/ui/episodes.go

@@ -257,7 +257,32 @@ func (v *seriesView) renderDetail() {
 			sum = se
 		}
 	}
-	v.detail.Show(seriesRowDetail(v.series, r.ep, r.season, sum, v.seasonMonitored(r.season), time.Now().Format("2006-01-02")), v.cover)
+	v.detail.Show(seriesRowDetail(v.series, r.ep, r.season, sum, v.seasonMonitored(r.season), time.Now().Format("2006-01-02")), v.seasonCover(r.season))
+}
+
+// seasonCover is the poster of a season, for its row and its episodes: the
+// season's own poster where Sonarr has one (a TheTVDB link, fetched without
+// credentials), else, or when it cannot be loaded, the series poster.
+func (v *seriesView) seasonCover(season int) coverRef {
+	for _, se := range v.series.Seasons {
+		if se.SeasonNumber != season {
+			continue
+		}
+		for _, img := range se.Images {
+			if img.CoverType != "poster" || img.RemoteURL == "" {
+				continue
+			}
+			remote, series := img.RemoteURL, v.cover
+			return coverRef{key: "season|" + remote, fetch: func(ctx context.Context, large bool) ([]byte, error) {
+				data, err := arr.FetchURL(ctx, remote)
+				if err != nil && series.fetch != nil {
+					return series.fetch(ctx, large)
+				}
+				return data, err
+			}}
+		}
+	}
+	return v.cover
 }
 
 // seriesRowDetail is the detail text of the drill-down: the series, then the