Implement macOS local MP3 discovery foundation

packages/apple/VelodyPersistence/Sources/VelodyPersistence/LocalMusicDiscovery.swift

@@ -0,0 +1,35 @@
+import Foundation
+import VelodyDomain
+
+public struct LocalTrackMetadata: Hashable, Sendable {
+    public var title: String?
+    public var artist: String?
+    public var album: String?
+    public var durationSeconds: Double?
+
+    public init(
+        title: String? = nil,
+        artist: String? = nil,
+        album: String? = nil,
+        durationSeconds: Double? = nil
+    ) {
+        self.title = title
+        self.artist = artist
+        self.album = album
+        self.durationSeconds = durationSeconds
+    }
+}
+
+@MainActor
+public protocol FolderAccessService: AnyObject {
+    func chooseFolder() -> URL?
+    func storedFolderURL() -> URL?
+}
+
+public protocol MetadataReader {
+    func readMetadata(for fileURL: URL) async throws -> LocalTrackMetadata
+}
+
+public protocol LocalMusicScanner {
+    func scanFolder(at folderURL: URL) async throws -> [LibraryTrack]
+}