Posters: fetch TheMovieDB images at the shown size, not the original

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

internal/arr/image_test.go

@@ -8,6 +8,23 @@ import (
 	"testing"
 )
 
+func TestTMDBSized(t *testing.T) {
+	for _, tc := range []struct {
+		in    string
+		large bool
+		want  string
+	}{
+		{"https://image.tmdb.org/t/p/original/abc.jpg", true, "https://image.tmdb.org/t/p/w780/abc.jpg"},
+		{"https://image.tmdb.org/t/p/original/abc.jpg", false, "https://image.tmdb.org/t/p/w342/abc.jpg"},
+		{"https://image.tmdb.org/t/p/w500/abc.jpg", true, "https://image.tmdb.org/t/p/w500/abc.jpg"},
+		{"https://artworks.thetvdb.com/banners/posters/1.jpg", true, "https://artworks.thetvdb.com/banners/posters/1.jpg"},
+	} {
+		if got := tmdbSized(tc.in, tc.large); got != tc.want {
+			t.Errorf("tmdbSized(%q, %v) = %q, want %q", tc.in, tc.large, got, tc.want)
+		}
+	}
+}
+
 func TestScaledVariant(t *testing.T) {
 	for _, tc := range []struct {
 		in    string