feat: implement queue management system

- Add QueueManager in Rust backend with shuffle, repeat modes, and history
- Create queue Tauri commands (add, remove, next, previous, play_index, etc.)
- Wire Next/Previous buttons to backend queue
- Auto-advance to next track when current track ends
- Sync queue state with frontend QueuePanel
- Wire shuffle and repeat toggles to backend
- Add queue population when playing from album detail view

src-tauri/src/commands/mod.rs

@@ -4,8 +4,10 @@
 
 pub mod auth;
 pub mod playback;
+pub mod queue;
 pub mod search;
 
 pub use auth::*;
 pub use playback::*;
+pub use queue::*;
 pub use search::*;