add Sparkle appcast

Sources/ViewModels/SparkleUpdater.swift

@@ -0,0 +1,26 @@
+import Sparkle
+import Foundation
+
+@MainActor
+final class SparkleUpdater: NSObject, ObservableObject {
+    let controller: SPUStandardUpdaterController
+
+    override init() {
+        self.controller = SPUStandardUpdaterController(startingUpdater: true, updaterDelegate: nil, userDriverDelegate: nil)
+        super.init()
+    }
+
+    var automaticallyChecksForUpdates: Bool {
+        get { controller.updater.automaticallyChecksForUpdates }
+        set { controller.updater.automaticallyChecksForUpdates = newValue }
+    }
+
+    var automaticallyDownloadsUpdates: Bool {
+        get { controller.updater.automaticallyDownloadsUpdates }
+        set { controller.updater.automaticallyDownloadsUpdates = newValue }
+    }
+
+    func checkForUpdates() {
+        controller.checkForUpdates(nil)
+    }
+}