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.go

@@ -46,6 +46,9 @@ type Season struct {
 	SeasonNumber int        `json:"seasonNumber"`
 	Monitored    bool       `json:"monitored"`
 	Statistics   Statistics `json:"statistics"`
+	// Images are the season's posters, only filled by GetSeries; Sonarr keeps
+	// no copy of them, so they only have a remote URL (TheTVDB).
+	Images []arr.Image `json:"images,omitempty"`
 }
 
 // Statistics are the episode counts Sonarr reports for library series.
@@ -179,7 +182,8 @@ func (c *Client) SearchEpisode(ctx context.Context, episodeID int) error {
 // GetSeries fetches one library series.
 func (c *Client) GetSeries(ctx context.Context, id int) (Series, error) {
 	var s Series
-	err := c.Do(ctx, http.MethodGet, "series/"+strconv.Itoa(id), nil, nil, &s)
+	// Season posters are only sent when asked for.
+	err := c.Do(ctx, http.MethodGet, "series/"+strconv.Itoa(id), url.Values{"includeSeasonImages": {"true"}}, nil, &s)
 	return s, err
 }