feat(credits): add Album Credits Modal (Phase 4)

- Add get_album_credits Tauri command with TrackCredits, AlbumCredits,
  and AlbumInfo structs for consolidated album/track credits view
- Create AlbumCreditsModal component with two-column layout:
  album info (artwork, metadata, quality badges) and collapsible
  track list with performers and copyright
- Add Info button to AlbumDetailView header actions
- Integrate modal in +page.svelte with track play support

src-tauri/src/commands/mod.rs

@@ -6,6 +6,7 @@ pub mod audio_backends;
 pub mod audio_diagnostics;
 pub mod auth;
 pub mod cache;
+pub mod credits;
 pub mod favorites;
 pub mod lastfm;
 pub mod notification;
@@ -22,6 +23,7 @@ pub use audio_backends::*;
 pub use audio_diagnostics::*;
 pub use auth::*;
 pub use cache::*;
+pub use credits::*;
 pub use favorites::*;
 pub use lastfm::*;
 pub use notification::*;