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/app.rs

@@ -1,6 +1,8 @@
 use anyhow::Result;
 use ratatui::widgets::ListState;
+use std::path::PathBuf;
 
+use crate::config::Config;
 use crate::emby::{Client, Item};
 use crate::player::Player;
 
@@ -40,10 +42,20 @@ pub struct App {
     /// brings you to the same season/series row, not row 0).
     pub selection_stack: Vec<usize>,
     pub status: String,
+    /// Live, editable configuration. Mirrors what's on disk; the settings
+    /// screen mutates this and persists it through `config_path`.
+    pub config: Config,
+    /// Where to persist updated settings. `None` when no writable location was
+    /// determined (rare; the settings screen will then refuse to save).
+    pub config_path: Option<PathBuf>,
 }
 
 impl App {
-    pub async fn new(client: Client) -> Result<Self> {
+    pub async fn new(
+        client: Client,
+        config: Config,
+        config_path: Option<PathBuf>,
+    ) -> Result<Self> {
         let libraries = client.views().await?;
         // Best-effort: don't fail startup if the resume endpoint hiccups.
         let resume = client.resume_items(20).await.unwrap_or_default();
@@ -72,6 +84,8 @@ impl App {
             breadcrumbs: vec![],
             selection_stack: vec![],
             status,
+            config,
+            config_path,
         })
     }
 
@@ -228,7 +242,10 @@ impl App {
                 self.status = format!("Playing {title}...");
                 let start_seconds = (*start_ticks as f64) / 10_000_000.0;
                 let reporter = self.client.reporter(id.clone());
-                let mut player = Player::new()?;
+                let mut player = Player::new(
+                    self.config.audio_lang.as_deref(),
+                    self.config.subtitle_lang.as_deref(),
+                )?;
                 let r = player.play_blocking(&url, title, start_seconds, Some(&reporter));
                 self.status = match &r {
                     Ok(_) => format!("Finished: {title}"),
@@ -261,7 +278,7 @@ fn restore_selection(saved: Option<usize>, len: usize) -> Option<usize> {
     Some(saved.unwrap_or(0).min(len - 1))
 }
 
-fn build_home_entries(libraries: &[Item], resume: &[Item]) -> Vec<Item> {
+pub(crate) fn build_home_entries(libraries: &[Item], resume: &[Item]) -> Vec<Item> {
     let mut entries: Vec<Item> = Vec::with_capacity(libraries.len() + 1);
     if !resume.is_empty() {
         entries.push(Item {