feat: add Playlist and PlaylistTrack models

Music/Models/Playlist.swift

@@ -0,0 +1,28 @@
+import Foundation
+import GRDB
+
+nonisolated struct Playlist: Codable, Identifiable, Equatable, Hashable, Sendable {
+    var id: Int64?
+    var name: String
+    var createdAt: Date
+}
+
+nonisolated extension Playlist: FetchableRecord, MutablePersistableRecord {
+    static let databaseTableName = "playlists"
+
+    mutating func didInsert(_ inserted: InsertionSuccess) {
+        id = inserted.rowID
+    }
+}
+
+#if DEBUG
+extension Playlist {
+    static func fixture(
+        id: Int64? = nil,
+        name: String = "Test Playlist",
+        createdAt: Date = Date()
+    ) -> Playlist {
+        Playlist(id: id, name: name, createdAt: createdAt)
+    }
+}
+#endif

Music/Models/PlaylistTrack.swift

@@ -0,0 +1,17 @@
+import Foundation
+import GRDB
+
+nonisolated struct PlaylistTrack: Codable, Identifiable, Equatable, Hashable, Sendable {
+    var id: Int64?
+    var playlistId: Int64
+    var trackId: Int64
+    var position: Int
+}
+
+nonisolated extension PlaylistTrack: FetchableRecord, MutablePersistableRecord {
+    static let databaseTableName = "playlist_tracks"
+
+    mutating func didInsert(_ inserted: InsertionSuccess) {
+        id = inserted.rowID
+    }
+}