Issue #3: Added Settings class to store selected BlocklistOption. Update system DoH settings, when user selects another blocklist.

dns/Settings.swift

@@ -0,0 +1,24 @@
+//
+//  Settings.swift
+//  dns
+//
+//  Created by Benjamin Erhart on 15.04.26.
+//
+
+import Foundation
+
+class Settings {
+
+    private static let blocklistKey = "blocklist"
+
+    private static let defaults = UserDefaults.standard
+
+    class var blocklist: BlocklistOption {
+        get {
+            BlocklistOption(rawValue: defaults.string(forKey: blocklistKey) ?? BlocklistOption.secure.rawValue) ?? .secure
+        }
+        set {
+            defaults.set(newValue.rawValue, forKey: blocklistKey)
+        }
+    }
+}