feat(library): extract and display album artwork

- Extract embedded artwork from audio files during scan
- Save extracted artwork to cache directory (~/.cache/qbz/artwork)
- Fallback to folder artwork (cover.jpg, folder.jpg, front.jpg, etc.)
- Add get_artwork_cache_dir helper function
- Artwork now displays in album cards and detail views

src-tauri/src/library/commands.rs

@@ -6,7 +6,7 @@ use tauri::State;
 use tokio::sync::Mutex;
 
 use crate::library::{
-    cue_to_tracks, CueParser, LibraryDatabase, LibraryError, LibraryScanner, LibraryStats,
+    cue_to_tracks, get_artwork_cache_dir, CueParser, LibraryDatabase, LibraryScanner, LibraryStats,
     LocalAlbum, LocalArtist, LocalTrack, MetadataExtractor, ScanError, ScanProgress, ScanStatus,
 };
 
@@ -158,7 +158,15 @@ pub async fn library_scan(state: State<'_, LibraryState>) -> Result<(), String>
             }
 
             match MetadataExtractor::extract(audio_path) {
-                Ok(track) => {
+                Ok(mut track) => {
+                    // Try to extract embedded artwork, fallback to folder artwork
+                    let artwork_cache = get_artwork_cache_dir();
+                    if let Some(artwork_path) = MetadataExtractor::extract_artwork(audio_path, &artwork_cache) {
+                        track.artwork_path = Some(artwork_path);
+                    } else if let Some(folder_art) = MetadataExtractor::find_folder_artwork(audio_path) {
+                        track.artwork_path = Some(folder_art);
+                    }
+
                     let db = state.db.lock().await;
                     if let Err(e) = db.insert_track(&track) {
                         all_errors.push(ScanError {

src-tauri/src/library/metadata.rs

@@ -197,6 +197,31 @@ impl MetadataExtractor {
         }
         hash
     }
+
+    /// Look for folder artwork (cover.jpg, folder.jpg, etc.)
+    /// Returns the path if found
+    pub fn find_folder_artwork(audio_file_path: &Path) -> Option<String> {
+        let parent_dir = audio_file_path.parent()?;
+
+        // Common artwork filenames in order of preference
+        const ARTWORK_NAMES: &[&str] = &[
+            "cover.jpg", "cover.jpeg", "cover.png",
+            "folder.jpg", "folder.jpeg", "folder.png",
+            "front.jpg", "front.jpeg", "front.png",
+            "album.jpg", "album.jpeg", "album.png",
+            "Cover.jpg", "Cover.jpeg", "Cover.png",
+            "Folder.jpg", "Folder.jpeg", "Folder.png",
+        ];
+
+        for name in ARTWORK_NAMES {
+            let artwork_path = parent_dir.join(name);
+            if artwork_path.exists() {
+                return Some(artwork_path.to_string_lossy().to_string());
+            }
+        }
+
+        None
+    }
 }
 
 #[cfg(test)]

src-tauri/src/library/mod.rs

@@ -32,6 +32,16 @@ pub fn get_db_path() -> PathBuf {
     data_dir.join("library.db")
 }
 
+/// Get artwork cache directory
+pub fn get_artwork_cache_dir() -> PathBuf {
+    let cache_dir = dirs::cache_dir()
+        .unwrap_or_else(|| PathBuf::from("."))
+        .join("qbz")
+        .join("artwork");
+    std::fs::create_dir_all(&cache_dir).ok();
+    cache_dir
+}
+
 /// Initialize library state
 pub fn init_library_state() -> Result<LibraryState, LibraryError> {
     let db_path = get_db_path();