Add default audio/subtitle language config and in-TUI settings editor

* New audio_lang / subtitle_lang fields in config (file, CLI flags, env
  vars). Forwarded to mpv's alang/slang as a comma-separated ISO 639
  priority list, e.g. "jpn,eng".
* New Settings screen (press `s` in the main view) for editing server,
  user, password, and language preferences without leaving the app.
  Credential changes trigger re-authentication against the new endpoint;
  on success the libraries/resume list is refreshed. Everything is
  persisted back to the config file the app loaded from.

Co-Authored-By: Claude Opus 4.7 (1M context) <[email protected]>

src/config.rs

@@ -18,6 +18,16 @@ pub struct CliArgs {
     #[arg(short, long, env = "EMBY_PASSWORD")]
     pub password: Option<String>,
 
+    /// Preferred audio language(s), comma-separated ISO 639 codes (e.g. "jpn,eng").
+    /// Forwarded to mpv's `alang`.
+    #[arg(long, env = "EMBY_AUDIO_LANG")]
+    pub audio_lang: Option<String>,
+
+    /// Preferred subtitle language(s), comma-separated ISO 639 codes (e.g. "eng,jpn").
+    /// Forwarded to mpv's `slang`.
+    #[arg(long, env = "EMBY_SUBTITLE_LANG")]
+    pub subtitle_lang: Option<String>,
+
     /// Path to config file. Defaults: ./config.toml then $XDG_CONFIG_HOME/emby-client/config.toml
     #[arg(short, long)]
     pub config: Option<PathBuf>,
@@ -32,6 +42,8 @@ pub struct FileConfig {
     pub server: Option<String>,
     pub user: Option<String>,
     pub password: Option<String>,
+    pub audio_lang: Option<String>,
+    pub subtitle_lang: Option<String>,
 }
 
 #[derive(Debug, Clone)]
@@ -39,24 +51,26 @@ pub struct Config {
     pub server: String,
     pub user: String,
     pub password: String,
+    pub audio_lang: Option<String>,
+    pub subtitle_lang: Option<String>,
 }
 
-/// Returns `(Some(config), save_target)` when all credentials are available,
-/// or `(None, save_target)` when at least one is missing — the caller can then
-/// prompt the user. `save_target` is the path where new credentials should
-/// be persisted if the user chooses to save them.
 pub fn load(args: &CliArgs) -> Result<(Option<Config>, Option<PathBuf>)> {
     let (file_cfg, save_target) = read_file_config(args.config.as_deref())?;
 
     let server = args.server.clone().or(file_cfg.server);
     let user = args.user.clone().or(file_cfg.user);
     let password = args.password.clone().or(file_cfg.password);
+    let audio_lang = args.audio_lang.clone().or(file_cfg.audio_lang);
+    let subtitle_lang = args.subtitle_lang.clone().or(file_cfg.subtitle_lang);
 
     let cfg = match (server, user, password) {
         (Some(server), Some(user), Some(password)) => Some(Config {
             server: server.trim_end_matches('/').to_string(),
             user,
             password,
+            audio_lang,
+            subtitle_lang,
         }),
         _ => None,
     };
@@ -108,6 +122,8 @@ pub fn save(path: &Path, cfg: &Config) -> Result<()> {
         server: Some(cfg.server.clone()),
         user: Some(cfg.user.clone()),
         password: Some(cfg.password.clone()),
+        audio_lang: cfg.audio_lang.clone(),
+        subtitle_lang: cfg.subtitle_lang.clone(),
     };
     let text = toml::to_string_pretty(&file_cfg).context("serializing config")?;
     std::fs::write(path, text).with_context(|| format!("writing {}", path.display()))?;