feat: add LibraryViewModel.applyTrackEdits

Music/ViewModels/LibraryViewModel.swift

@@ -11,14 +11,29 @@ final class LibraryViewModel {
     var trackCount = 0
 
     private let db: DatabaseService
+    private let editService: TrackEditService
     private var cancellable: AnyDatabaseCancellable?
     private var searchTask: Task<Void, Never>?
 
     init(db: DatabaseService) {
         self.db = db
+        self.editService = TrackEditService(database: db)
         updateQuery()
     }
 
+    // Applies metadata edits to one or more tracks. File-tag writes run off the
+    // main actor; the library list refreshes automatically via the DB observation
+    // (no manual reload). Returns per-track warnings (unsupported format / file
+    // write failure) for the caller to surface; the DB edit always lands.
+    func applyTrackEdits(
+        _ values: EditableTrackFields,
+        editing edited: Set<EditableTrackField>,
+        to tracks: [Track]
+    ) async -> [TrackEditWarning] {
+        let service = editService
+        return await Task.detached { service.save(values, editing: edited, to: tracks) }.value
+    }
+
     func search(_ text: String) {
         searchText = text
         searchTask?.cancel()