Workstream C: extract player settings and queue-manipulation commands into submodules

- commands/player/settings.rs: audio/video settings commands (4).
- commands/player/queue.rs: queue add/remove/move/skip + by-id commands (6) and
  their request DTOs.
- Make check_for_local_download and get_queue_status pub(super) for reuse.
- mod.rs now ~1834 lines (from 2720); invoke_handler unchanged, all tests pass.

src-tauri/src/commands/player/settings.rs

@@ -0,0 +1,58 @@
+//! Audio and video playback settings commands.
+
+use tauri::State;
+
+use super::{PlayerStateWrapper, VideoSettingsWrapper};
+use crate::player::AutoplaySettings;
+use crate::settings::{AudioSettings, VideoSettings};
+
+#[tauri::command]
+pub async fn player_set_audio_settings(
+    player: State<'_, PlayerStateWrapper>,
+    settings: AudioSettings,
+) -> Result<AudioSettings, String> {
+    let mut controller = player.0.lock().await;
+    controller
+        .set_audio_settings(&settings)
+        .map_err(|e| e.to_string())?;
+    Ok(controller.audio_settings())
+}
+
+#[tauri::command]
+pub async fn player_get_audio_settings(
+    player: State<'_, PlayerStateWrapper>,
+) -> Result<AudioSettings, String> {
+    let controller = player.0.lock().await;
+    Ok(controller.audio_settings())
+}
+
+#[tauri::command]
+pub async fn player_set_video_settings(
+    video_settings: State<'_, VideoSettingsWrapper>,
+    player: State<'_, PlayerStateWrapper>,
+    settings: VideoSettings,
+) -> Result<VideoSettings, String> {
+    let validated = settings.with_countdown_clamped();
+    {
+        let mut current = video_settings.0.lock().map_err(|e| e.to_string())?;
+        *current = validated.clone();
+    } // Drop MutexGuard before await
+
+    // Sync to PlayerController's autoplay settings so on_playback_ended() uses current values
+    let controller = player.0.lock().await;
+    controller.set_autoplay_settings(AutoplaySettings {
+        enabled: validated.auto_play_next_episode,
+        countdown_seconds: validated.auto_play_countdown_seconds,
+        max_episodes: validated.auto_play_max_episodes,
+    });
+
+    Ok(validated)
+}
+
+#[tauri::command]
+pub async fn player_get_video_settings(
+    video_settings: State<'_, VideoSettingsWrapper>,
+) -> Result<VideoSettings, String> {
+    let current = video_settings.0.lock().map_err(|e| e.to_string())?;
+    Ok(current.clone())
+}