Add source/qobuz_track_id to LocalTrack model and implement filtering for Artists/Tracks

- Added source and qobuz_track_id fields to LocalTrack model for proper filtering
- Updated all database row mapping functions to include new fields
- Implemented network folder and download filtering for library_get_artists command
- Implemented network folder and download filtering for library_search (Tracks) command
- Made tab counters (Albums, Artists, Tracks) reactive to filtered content
- Counters now update based on current filtered data instead of total stats

Fixes offline mode filtering for Artists and Tracks tabs. When offline or when
downloads are hidden, Artists/Tracks now properly filter out inaccessible content,
matching the behavior already implemented for Albums.

src-tauri/src/library/models.rs

@@ -72,6 +72,10 @@ pub struct LocalTrack {
     // Indexing
     pub last_modified: i64,
     pub indexed_at: i64,
+
+    // Download tracking
+    pub source: Option<String>,
+    pub qobuz_track_id: Option<i64>,
 }
 
 impl Default for LocalTrack {
@@ -102,6 +106,8 @@ impl Default for LocalTrack {
             artwork_path: None,
             last_modified: 0,
             indexed_at: 0,
+            source: None,
+            qobuz_track_id: None,
         }
     }
 }