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/sonarr/sonarr_test.go

@@ -198,3 +198,23 @@ func TestCalendar(t *testing.T) {
 		t.Errorf("episode not decoded: %+v", e)
 	}
 }
+
+func TestGetSeriesAsksForSeasonPosters(t *testing.T) {
+	var query string
+	srv := httptest.NewServer(http.HandlerFunc(func(w http.ResponseWriter, r *http.Request) {
+		query = r.URL.RawQuery
+		w.Write([]byte(`{"id":7,"title":"Andor","seasons":[{"seasonNumber":1,"monitored":true,
+			"images":[{"coverType":"poster","remoteUrl":"https://artworks.thetvdb.com/banners/seasons/1.jpg"}]}]}`))
+	}))
+	defer srv.Close()
+	s, err := NewClient(srv.URL, "k").GetSeries(t.Context(), 7)
+	if err != nil {
+		t.Fatal(err)
+	}
+	if query != "includeSeasonImages=true" {
+		t.Errorf("query %q", query)
+	}
+	if len(s.Seasons) != 1 || len(s.Seasons[0].Images) != 1 || s.Seasons[0].Images[0].RemoteURL == "" {
+		t.Errorf("season images %+v", s.Seasons)
+	}
+}