WIP: add Dock visibility setting

tests/clipboredtests/SettingsModelTests.swift

@@ -0,0 +1,28 @@
+import XCTest
+@testable import ClipBored
+
+final class SettingsModelTests: XCTestCase {
+  func testShowDockIconPersistsAndNotifies() {
+    let suiteName = "com.clipbored.settingsmodel.\(UUID().uuidString)"
+    let defaults = UserDefaults(suiteName: suiteName)!
+    defer {
+      defaults.removePersistentDomain(forName: suiteName)
+    }
+    let settings = SettingsModel(defaults: defaults)
+    var changes: [SettingsModel.Change] = []
+    settings.observe { changes.append($0) }
+
+    XCTAssertFalse(settings.showDockIcon)
+
+    settings.showDockIcon = true
+
+    XCTAssertTrue(defaults.bool(forKey: SettingsModel.Keys.showDockIcon))
+    XCTAssertEqual(changes.count, 1)
+    guard case .showDockIcon = changes.first else {
+      return XCTFail("Expected showDockIcon change notification")
+    }
+
+    let restored = SettingsModel(defaults: defaults)
+    XCTAssertTrue(restored.showDockIcon)
+  }
+}