feat(macos): add native menu bar app with notch overlay

Introduces a SwiftUI companion app for the Fail Well PWA: menu bar
status item, popover with task list / record / history views, command
palette, and a Dynamic Island-style notch overlay that shows the active
step and timer beside the hardware notch and expands on hover to reveal
pause/next controls.

macos/Sources/FailWell/Models/Step.swift

@@ -0,0 +1,8 @@
+import Foundation
+
+struct Step: Codable, Identifiable, Hashable, Sendable {
+    let id: String
+    var title: String
+    /// estimation in minutes
+    var estimation: Int
+}