feat(jellyfin): add config flag and URL path constant

Adds the disabled-by-default Server.Jellyfin config option (Enabled,
ServerName) and consts.URLPathJellyfinAPI, following the existing
LastFM/ListenBrainz patterns. Later tasks will use these to mount the
Jellyfin-compatible API router.

conf/configuration.go

@@ -116,6 +116,7 @@ type configOptions struct {
 	LastFM                          lastfmOptions       `json:",omitzero"`
 	Deezer                          deezerOptions       `json:",omitzero"`
 	ListenBrainz                    listenBrainzOptions `json:",omitzero"`
+	Jellyfin                        jellyfinOptions     `json:",omitzero"`
 	EnableScrobbleHistory           bool
 	Tags                            map[string]TagConf `json:",omitempty"`
 	Agents                          string
@@ -218,6 +219,11 @@ type listenBrainzOptions struct {
 	TrackAlgorithm  string
 }
 
+type jellyfinOptions struct {
+	Enabled    bool
+	ServerName string
+}
+
 type httpHeaderOptions struct {
 	FrameOptions string
 }
@@ -577,6 +583,7 @@ func disableExternalServices() {
 	Server.LastFM.Enabled = false
 	Server.Deezer.Enabled = false
 	Server.ListenBrainz.Enabled = false
+	Server.Jellyfin.Enabled = false
 	Server.Agents = ""
 	if Server.UILoginBackgroundURL == consts.DefaultUILoginBackgroundURL {
 		Server.UILoginBackgroundURL = consts.DefaultUILoginBackgroundURLOffline
@@ -848,6 +855,8 @@ func setViperDefaults() {
 	viper.SetDefault("listenbrainz.baseurl", consts.DefaultListenBrainzBaseURL)
 	viper.SetDefault("listenbrainz.artistalgorithm", consts.DefaultListenBrainzArtistAlgorithm)
 	viper.SetDefault("listenbrainz.trackalgorithm", consts.DefaultListenBrainzTrackAlgorithm)
+	viper.SetDefault("jellyfin.enabled", false)
+	viper.SetDefault("jellyfin.servername", consts.AppName)
 	viper.SetDefault("enablescrobblehistory", true)
 	viper.SetDefault("httpheaders.frameoptions", "DENY")
 	viper.SetDefault("backup.path", "")

consts/consts.go

@@ -44,6 +44,7 @@ const (
 	URLPathSubsonicAPI  = "/rest"
 	URLPathPublic       = "/share"
 	URLPathPublicImages = URLPathPublic + "/img"
+	URLPathJellyfinAPI  = "/jellyfin"
 
 	// DefaultUILoginBackgroundURL uses Navidrome curated background images collection,
 	// available at https://unsplash.com/collections/20072696/navidrome